Maybe you could help me.

Hayleigh
I am a 16 year old girl. and my periods are a little wacky. I am not on birth control when I probably should be. My periods always change their dates. As in, they are always on time. They either come a little early or late; but not like late-late. Just maybe one to three days later. I have had sex and that just made them a little wackier. 
Do any of you know what i should do ?