2 almost 3 week long period w/ spotting!!! HELP!

I've read some of the other posts but mine is a little different. I'm 17 years old... and I'm sexually active.. ALL OF IT PROTECTED. And we check the condom for any tears or holes afterwards... Well I started my period on June 13, 2007, very light flow... which is unusual for me cause my periods are usually very heavy with very bad cramping! June 23rd 2007 i marked on my calendar i was still bleeding.. light flow still... June 25th, still bled.. but spotting.. like bled a little in the morning and it stopped for the rest of the day.. that same day i had intercourse... protected.. and we checked the condom.. no tears or anything.. June 26th.. spotting.. and then no period for a couple days.. Today is July 2nd 2007, and I was cleaning earlier today.. and it felt like just normal discharge... when i was cleaning like.. it felt like tiny bubbles of air.. so i figured it was just normal discharge.. but then my boyfriend and i were going to have oral sex.. and he thought i was really wet... but i pulled down my panties.. and looked and my panties are covered with blood. SEMI HEAVY BLEEDING... but no cramps at all.. and like i said before.. i usually have really bad cramps.. so .. Before JUNE 13TH 2007 MY FIRST PERIOD.. i took a pregnancy test.. came back negative.. then a few days later... I took another.. still negative... WHAT COULD BE WRONG WITH ME?!?!?!?! Please help!

I'm not on any medication... no birth control or anything.. My boyfriend and i have sex rarely.. I once was checked for having really really bad cramping in my lower stomach.. and turned out i had a cyst.. it went away on its own.. i don't know what it could be... PLEASE PLEASE HELP if you know anything about this at all!

Thanks.