3 month old ball python eating problems & possibly sick? Need advice

I'm still very new to owning a snake.
I usually have my day time lamp on all the time only because it keeps the temperature on the high side on between 80-88, my low side is usually in the mid 70's. The humidity is usually 40-55. His enclosure is a tank but it's on the counter of my room and is pretty isolated as my bed and dresser cover the sides. He completed his shed probably around a month ago. I do not know his weight but he is pretty skinny but I have been trying to make sure his feeding schedule is good so he gets fatter (usually one to two fuzzies a week besides the time he was shedding) I do have a bit of trouble with feeding. He hasn't ate in the past three weeks and it makes me worried. At first he missed it when he striked at it, so I figured he wouldn't want to eat for a bit. Few days later I try again- didn't work. So I wait about 5-7 days and try again. unsuccesful. Each time he looks like he's hungry and he wants to eat it, he even follows it around a bit but he just doesn't strike at it. Instead he lays his head on it. He has always ate frozen for his entire life and he hasn't had much of a struggle with it. I know it's winter so they may not eat for a while but I live in Florida, so I figured it may not affect him. Is he going into another shed? I read somewhere that baby ball pythons can shed up to every 3 weeks. I just had his first shed with me not too long ago so I don't think that's it. We were moving, could that have stressed him out. He was only in the car for five minutes (we didn't move very far) but he wasn't eating before that. I haven't been handling him lately, I am just really handling him today after a week of barely touching him. I thought he might be dehydrated so I got some warm (not hot like Luke warm) and let him soak in it for one minute. He didn't seem to mind at first then he wanted to get out so I let him (he was in a plastic container). I worry about how much he eats so much because he doesn't have a lot of body weight and his spine shows. I bought him at Petco and he was hungry and covered in mites. We fixed the problem right away but he hasn't gained much weight. I got him around two months ago.

My first thought is the prey is not warm enough or cooling to much before being presented. How are you thawing and warming the prey?

I use warm water to thaw and then hot water to warm. The live body temp of a mouse is around 100F so the f/t needs to be presented at the same to mimic a meal.

Other than that it could be a whole list of things. Adding some pics of the setup and the snake could help narrow things down.

I use cold water for about 30-40 minutes then I dry it and blow dry it a bit to make it warm. I have done it before and it hasn't bothered him. I used to switch it from cold water so it thaws out a bit then warm water and blow dry it. It also worked for me. I did the first thing and I have been doing it, he just hasn't been accepting it. Should I start using warm water? I was afraid to because I had heard it could cause blizzards on the mouse because it would heat up too fast and it could harm the snake. I read about it on a care sheet.

I'm not sure how to add pictures otherwise I would. He has two hides on each side along with a branch. It has stickers on it (the ones you buy to make the tank look nice) so the back is covered. He has a coconut substrate I believe. He also has some fake plants on both sides. His water is in the middle and the day time lamp is on the hot side. He usually stays hidden in his hide on the hot side. Sometimes he moves around during the day time but that's usually when his cold side reaches the low 80's so I turn off the day lamp and sometimes spray water to both increase the humidity and decrease the temperature. It helps. I used to have problems with humidity and it would go 20-30% but I recently found out that if its on the ground it stays 50% without having me to constantly spray the tank.

Hot water from the tap is fine. That's what I use. Snakes can be weird and though it took a few when you first got it doesn't mean it wont just stop taking them for a silly reason. I say heat it better and see how it goes. Heat it in the hot water and use a IR temp gun to check the temp if you have one. You really want it to be over 100F because they start to cool quickly. You want to be able to give the prey a squeeze and feel insides are thoroughly warmed.

I would think that your snake could take larger prey than a hopper but not seeing it I wont discuss that until we know more. It not really important what it eats as long as it eats. It would just be easier to be able to feed one mouse instead of two or three.

There are a few ways to post pics but I only know how to upload to Photobucket and then past the IMG code into your post. When you submit the post it will turn into a pic in the thread,

He is pretty small but the baby mouse or fuzzie (I don't know the correct terms) is usually an inch but I have gotten pretty big ones from the same bag. I will try to heat it up more, hopefully that will do. I tried to feed him yesterday, how long should I wait before trying again? I love having a RI gun they're so easy to use & read.

Trying to feed to often can add to the problems. When I get one that refuses I wait until the next scheduled feed day.

I would say to offer every 5-7 days.

Should I be worried since he's small?

I wouldn't think so. As long as it doesn't appear to be underweight for its size.

I had the same problem for awhile, except I was trying to switch mine over from live to f/t. He acted like he was afraid and refused to eat at all for about two and a half weeks. I used warm tap water to thaw the mouse, added a little chicken broth, and offered it to my snake. Wouldn't take it. I left it in the enclosure under the lamp for about an hour, went back and offered again-and bingo! He took it.