OK so I'm 14 and I have not started my period but I have had sex before and could that have something to do with it ?

No, being sexually active will not affect your period, just the rest of your life.

It's a sad commentary that you are sexually active at 14.

Be glad that your period hasn't started yet.
As for sex... you can't get virginity back, but you can get self-esteem back if you lost it just because you wanted to impress some guy or fell for some line he handed you. If you just wanted to see what it was like, what was it like? Not all it's cracked up to be, without the tenderness of true caring? You tell us. Hopefully you learned something, and will save sex for much later.