It's just not happening

So my fiancé and I have been trying to get pregnant for about 8 months now. I'm 23, no kids, and it's just not happening. My Gyn said it's because I've gained some weight recently, which I've been trying hard to lose but haven't made much progress yet. But I just don't know if that is the only answer. He won't run tests until I lose weight. I was on the depo for a few years, I've been on oral bc, which I've read could cause infertility. I just don't know why it's not happening for me.. anyone go through this? Advice?