Period & sex.

So I missed my period in November. And then so far in December I haven’t started yet. My boyfriend coming home from the navy in 2 weeks. And i haven’t seen him since may. So no I haven’t had sex with no other guy since then lol. I only been with him. There are days where I feel like I’m gonna start so I have a pad in my purse. But then I go to the bathroom and nothing. From my records I was suppose to start November 23. And I missed that period. And I’m afraid I’ll start at that same time when my bf home. Like omg! I’m trying to have sex lol. I need help like what am I doing wrong or can I start early.