I Have Been Taking Wellbutrin, Prozac, And Estrogen, Now My

I have been taking wellbutrin, prozac, and estrogen, Now my doctor has me on metformin for insulin resistence. I run/ walk an average of 15 miles a week. I have seen no change in my weight in over a year. Could all these medications have anything to do with it? I also stay on a very low carb diet. Drink a ton of water and one diet coke a day. Any advice would be helpful.