Someone once told me to wait about 6 months AFTER you start to get things in control before taking the plunge. I think it's a good rule of thumb. I made the mistake before of thinking I was ready when I wasn't.
My pdoc told me they weren't sure if the meds actually mess with your metabolism OR is it just that you are feeling better and not worrying so much that subconsciously, you aren't watching what you eat and maybe aren't as active. I put on about 40 lbs myself.
But, it is smart to do it under a doctor's care and do it at your own pace! I think that's MOST important