I've had Mr.Hide since summer of 2016. He was given to me in a pillow case by someone who was giving him away on kijiji. The woman didn't even let us come inside the apartment building, like she had something to hide. Anywho, we grabbed the pillow case, opened it to make sure it was a ball python, and left. Once in the car, we took the ball out, and let him explore. His body looked like he had been in a tight ball for a while, like it had trouble going back to ''normal''. He was underweight. The previous owner had been feeding him on live mice, and that was apparently the only thing he woud eat. He had stuck eye caps, and his eyes looked like broken glass. He looked dehydrated. Other than that, he was very curious. I worked on him slowly, soaked him every couple days, his eye caps came off fairly quickly, his scales are lustrous now. At first he was shedding almost scale by scale, now he sheds big patches at a time (I soak him when he's in shed).He could be anywhere between 3-5 years old. At first, he would eat every week, only live, but he ate mice, rats, and hamsters. I began weighing him in October 2016, at 935g, and in December he hit 1095g, and hasn't eaten since January. His weight is slowly going down, he's now at 1030g. I brought him to the vet just last week, it seems he could be starting a respiratory infection, so I medicate him every 3 days, over the course of one month. Here's my issue: he's a picky eater, and he's underweight, and has'nt eaten in almost 2 months. I know pythons can fast... but he's not at a healthy weight, which worries me. Somedays he'll refuse a rat, but will eat a mouse. Sometimes he'll refuse a mouse, but eat a hamster. Sometimes he'll eat rats. He gets scared of the mice/rats/hamsters sometimes, other times he'll go straight for them.

On a side note: I breed my own rats (for Ulysse the ball, and my 3 corns) and hamsters (just for Mr.Hide), but have given up breeding mice for the moment.

Basking spot: 32C, and he'll climb up the branches to get closer to the heat, where it gets to 35-40C. He has a heating wire, which I cover with newspaper so that it doesn't burn him.
Cool side: 22C
Humidity: 45-55% I've just added and humid hide.
Subtrate: Bark
Viv dimensions: 3foot x 18inches x 20inches (LxWxH)
Hiding spots in both cool and warm spots.
He has branches to climb on.
He's usually handled at least once a week. Will be handled every 3 days to administer meds.

He isn't severely underweight, but he's not plump like my other ball, and I've never seen a ball that thin/small.
Should I be worried? Should I just let time pass? Should I keep trying to feed him once a week, or should I distance his feedings out? Should he start eating again when he's hungry? Is there anything I should change about his husbandry? Should I maybe change him into an other vivarium? I have a 4'x18''x2' viv available.

I have another vet appointment on March 22nd to reexamine Mr.Hide, but I'm impatient for him to get better, gain some weight, and have some appetite!
Let me know what you think, what you know, what flaws you find in my set up. Thank you!