One and a half year old snake, 50 grams?

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I'd feed him one fuzzy per week, and I tried 2 in one week but he wasn't hungry.
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His Temps have always been fine, though it took about 2 weeks of tampering to get them right. He's at about 85 hot spot and 75 ambient, though now that winter is setting in, the Temps are fairly cold at night (working on a solution).
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Hes only shed twice since I got him, both times it was super stuck and he was wrinkly and dry as a corpse. I feel so bad. The vet tested him for parasites and it came out negative, however he gave me a dewormer anyway alongside antibiotics. After faithfully injecting him for a month, he's gained 10 grams.

First, are you sure that's an accurate weight? Hatchlings are born bigger than 55g.

Second, fuzzy what? Both mice and rat fuzzies are too small, but mice fuzzies are much smaller and would be far more of a setback to this point.

Third, stuck shed and super dry is a sign of bad humidity. You need to get an accurate humidity reading. Try to get the humidity up to around 50% for starters.

Fourth, I would bump the hotspot up at least a couple of degrees. 85 is on the very low end. Mine are only around 87 or 88, but 85 is pushing it.

If the weight is accurate and he's not sick or has parasites, the size is due to major underfeeding. Good news is this can be corrected extremely easily.