lost sex life

Me and my boyfriend have been together for just over six months and live together. He doesn't have to be into work until around 12 most days so he stays up late till around 1am but I have class every day around 830 so I got to bed between 11 and 12. We haven't had sex in a while we recently celebrated out 6 month anniversary and totally thought we were going to have sex that night but nothing happened. Any ideas on how to spice it up or bring it up in a way that doesn't seem to forced.