Welcome, Kitslag! I'm not from Hawaii but would LOVE to live there someday. It sounds so beautiful.
I also don't have any insightful things to say about your meds (only a physician is qualified to really discuss this with you), but wonder about a few things.
One is that could you maybe be worrying a bit too much about the effects of the meds on weight or even on the weight gain itself? It really hasn't been all that long since you had the surgery and your body's been through some changes. It's great that you gave up cigarettes, that was hard. You are getting healthier and isn't that more important right now than a weight gain, frustrating though that be. Could it be that when all your meds are sorted out and your body is stabilizing, your weight will stabilize?
Also, just wondering if 1200 calories is maybe a bit too low? Again, only a doc or maybe a dietician or nutritionist can advise on that. Sometimes people lose weight if they up the calories enough so the metabolism gets healthier.
Anyhow, good luck with your journey! Hope to see you regularly on the board!