Advice for Finally getting the Big O

I have been masterbating for about 7-8 years now and been sexually active for about 5-6. I have tried several different things to reach orgasm from just using my fingers to vibrators to oral and penetration sex. There has been a few times were I think I came really close but I never fully climaxed. I have had a few different partners and they tried to help me get there but eventually we gave up. At times, I've spent hours switching between clitoral stimulation and using a vibrator or my fingers to masterbate, and still haven't got there. I don't know what else I should try and do. I enjoy sex and it all feels good but I just can't seem to cum. Please help!