not so long lasting

so my boyfriend and I have been together for 7 months. We are living together for 2 months now. at first we had sex at least once a day for the first2 weeks. with him it doesn't last very long but I thought maybe if we have sex more he could last longer. well... 2 months later it still doesn't last. I can't even get into it because he's finished before I even get started! I am not use to this and I don't know what to do. I am sexually frustrated!