Thank you for posting your question here, I will try to answer it to the best of my abilities.
I recommend you see your doctor and ask if he can give you a higher dosage of levothyroxine
since the current dosage isnt working out for you, he may need to run a blood test
to check for what your current TSH
levels are first, but I think he will agree on increasing the dosage. Once he increases the dosage weight gain should go down as well.
I hope this answered your question.