Help meeeee

Jay
So awhile back, I would say around November I took plan B.. 7 days later I got  my period. & 3? Weeks after I had sex again & I haven't gotten my period yet. No the guy didn't cum in me. I'm just so worried. But my friend did tell me that plan b messes with your period cycle. So idk can anyone help me? Give me information. Or anything would be very well appreciate 
Thanks