my boyfriend won't have sex with me

Hi guys. So my boyfriend and I have been together 5 months and I would say we have a very active sex life. The past three weeks or so though he's had no interest in having sex. He says he gets nervous and that he doesn't want to be doing it all the time. Of course I agree that sex isn't all a romantic relationship should be, but I'm dying here. He knows what I want but he genuinely doesn't seem interested in anything. He's stressed and busy with work and school but I'm scared it's something else. Ami the only one this happens to? Should I be worried?