Sex advice?

So me and my significant other are living together now and at first we would have sex in the truck, couch, anywhere we could when we were together at first. But now after about 3 months it seems like he doesn't ever want to have sex. Maybe once ever 2-3 weeks. I'm a very sex driven woman and would like to have sex more often but he's always so tired and doesn't want to.

Also, when we do have sex it's only for about 15 minutes tops, and he gets off everytime. As for me, I have maybe once total..

Should I talk to him about it, ask for more? (Even though I know it will be excuses of why he doesnt like he's always so tired) or just go with it and enjoy the little bit I get, or do I cut him off and not have sex for a while?

I really love him but when it comes to sex it's usually all about his needs and not much attention towards my needs ever.

What do you guys think I should do?