Why can't I get pregnant! :(

Hi ladies I'm new to glow but been ttc for 2 an half years I'm 25 and my partner is 23.. I already have a little girl that's almost for and she's my everything but we both want more and she's even asking for a baby sister now :(. So anyway I've been to the docs and he says nothing's wrong I'm ovulating and my partner is fine to. I'm at that stage where I feel I'm going mad I mean it's the most nattral thing and I can't seem to do it. It's horrible to say but I'm seeing every1 preg ATM or just having babies I'm so jel. :(