I have another thread about this guy but I'm going to retire it because its a jumbled mess and I just want to update all my information and get it in one place. Also hoping it'll grab the attention of some fresh eyes.

Cosmo is my California kingsnake. He roughly a year old, I purchased him from petsmart a year ago for my boyfriend.
When we first got cosmo, he was 16 grams. I weighed him about once a month to keep track of his growth. He ate like a champ only skipping meals during shed. And yet... Cosmo, at his highest weight, only reached 24 grams at his highest weight. Ill admit... I took an incredibly long time to realize what's wrong with this and I only started to worry around September. But he ate fine so I just let him keep living his little runt life.

Well, at some point (I truly don't remember when this was now... october? Late September?) I ran out of pinkies. I had an order coming in like 2 weeks or something so to hold myself over i got some from petsmart. I got home and these pinks were on the larger side. But they still lacked fur and were packaged as pinkies. I'd also like to note that I'd read Cosmo should be on fuzzies at his age anyways, and there weren't too much bigger than what he ate, so I fed him one. He struggled a little but got it down. Next day, after work, I discover the pink in his cage. I realize my mistake of giving him something too large, wait about a week, normal sized pinks are shipped and feed him again. This meal stays down.

I wait one week, and with the 3rd meal, he regurges. Id have to fetch my book but I think I fed him 2 more time after this, he regurged, and I waited longer than a week and tried one more time with a tiny piece of mouse tail. Its nothing at all, but it was smaller than pink and it still didn't stay down. You don't have to tell me, I'm aware now I shouldve been waiting much longer. What's done is done.

After the mouse tail I rushed him to the vet a couple days afterward. Basically, the vet was confused about his size, and told me there wasn't tons to be done. He suggested a super diluted vitamin booster shot and a tube feed. I mentioned parasites, i got a little vial thing and we started to hope for poop so we could run tests on him.
Unfortunately, the liquid feed didn't even stay down, maybe 24hrs max.

After this I called up on the vet, and we decided to wait 2 weeks without bugging him at all. At this point he's lost significant amount of weight. Today, he was 14 grams. On Sunday I fed him, I cut the head off a pinkie. Even though again, it was a small meal, he couldn't keep it down.
He went back to the vet today... and... it wasn't good news. Hes obviously in significantly worse shape than the first time, incredibly lethargic, hasn't pooed (still getting urates tho). The vet really doesn't seem to think it's parasites, he thinks it's congenital and it's finally just starting to catch up to him. He's so sick now the vet thinks medication would do more harm than good, besides he literally doesn't have any meat anymore to inject anything into. Like... do I seriously just let him die. I don't want to tube feed him again, atleast, not until its been 2 weeks again. But he's so thin... idk what to do.