Try to look at what else might be different from before treatment that be contributing to weight gain. You shouldn't just keep gaining weight. Women after menopause can gain a little bit or slight fat distribution change but wouldnt normally be gaining continuously.
So consider :
Your exercise now as to before.
Dietry change from now and before.
As Brenda says...coffees, cappacinos etc can be sneaky extra cals.
Alcohol intake now as before.
Have you stopped smoking in this time?
Also worth discussing with GP and have a thyroid function test done to ensure all efficient.
Hope you find a solution soon. Kath x