My period was 8 days late and once I got it, it was only for 2 days?! (HELP!)?

So i need some help. My boyfriend and i had PROTECTED April 21st. Then i got my normal period (5 days) on May 1st. Then this month, (we didn't do anything) it was 8 days late.. Once i got it, it was only 2 days long, but I had it as a normal heavy flow.And two days in a row hen I wore a tampon to swim and last night (I march in Danbury Drum Corps) I marched two parades and then I went to the bathroom after and it was nothing.. I'm very scared because i am only 16 and i am not sure what is wrong with me. I even emailed Planned Parenthood and they don't think i am pregnant but i might have something else wrong. What do you think? PLEASE HELP!