Why does it take me so long to orgasm?????

I could enjoy the sex for the entire time and still not orgasm! I’m 24 and this has become a pattern. I’ve had three partners this year and only one of them has been able to get me to cum....but it still takes a long round (45 mins+) or round two. The last time we had sex It was tipsy sex during the night, didn’t cum, morning came and he gave me head with a little anal play and I came in about 15 mins....his penis used to get me to cum while I played with my clit....but hasn’t happened lately. Help?!?