I do not think you are having any reaction to the meds. Swelling is very common in hypos.
It is a magnesium depletion. Hypos bind magnesium and most of it is wasted out the urine. When you are low on mag - you bloat.
MAgnesium citrate twice daily works for me. Also stay off regular salt and go to unrefined sea salt.
Sea salt is totally a diretic and very healthy for adrenal support and thyroid support. It is even taking with a glass of filtered water 2x's a day for hormonal fatigue. I haven't started a regular regimen yet - but may start that soon.
I don't know about the allergy part, but I have Hashi's and the water retention and bloating is insane. I've never retained water like this. Limiting my sodium seems to help, but some days my lower legs are so swollen, it hurts to bend them--- feels like they're going to split!