Britt, it's nice to know someone my age who is single and still having sex! I miss it. lol
Anyway, I doubt the sex would make your period start sooner, but when I was close to my period and had sex, it would bring it on. Maybe it's the bumping against the cervix that causes it or having orgasms.
My periods got closer together at first, but now they are farther apart and shorter.
I'd talk to your doctor or gyno when you have your checkup about this.
Congrats on meeting a wonderful man. Maybe there's still hope for me!