My mom and one of my sisters had their thyroid removed and they didn't gain additional weight.
I didn't have to have my thyroid out but I take 100mcg of levothyroxene due to Hashimoto's Disease(had since my 20's).... and I think it has kept my weight balanced.
Maybe it's just too soon to tell yet for your body?? or it's some other med causing it??..

anyway-- I wish you the best. and hope you are recovering well.