My weight gain of 18 lbs was due to meds too

It is a real struggle to lose such weight gain... but it can be done.
I think the meds change our chemical makeup and how the body processes food???
Keep a food journal, so you are absolutely sure you aren't eating more than you used to ..or should.
Then it's back to basics... eat healthier, drink lots more water, and try to maintain your activity, if not increase it.
(I know everyone says there's nothing they can do about weight gain for cortisone... but I worked on that one, and found that you can keep from gaining on it... it causes you to be hungrier and you do eat more while on such a med...)
Good wishes on this!!! I know how depressing it is to gain weight while doing the right thing (taking a med for self care.)