Need all the help I can get.

Ok so I'm after some advice. Been TTC for 4 months now with no joy (I know compared to some people here that's not very long but for me it's a lifetime) and each and every time I get my period it's like my whole world comes crashing down. I live in the UK and was wondering if there is anything out there I could take to help with fertility? I've been told by my docs to take a multivitamin and folic acid but nothing else. Anyone got any ideas? Also, when should I think about using opk's?