Late period,negative tests,thirst and lethargy.

So, I shall give you the whole story, and everything else that may be helpful... My Last regular period was on April 26 (I think?? i can't really remember...) Anyway, my boyfriend and I had sex (well not really...it was in, without protection, for about 2 minutes im guessing. before we realized and stopped...) On May 21. On the 24th (about the time my next period should happen) I had what seemed right away to be a period but i didn't have cramps or any normal symptoms. I also bled much less than I normally do right away, and this lasted 2 days, and one really light day, and then was over. (it normally lasts 5 days..) I thought maybe it was just a fluke, and waited for my next to be sure. (during this time we did the same thing as described above two more times...duno if that matters at all.) My next period was supposed to be around June 21, but never came. I am now almost 2 weeks late, and getting fairly worried...I have taken 2 preg tests, one on the 23, one on July 1. and both were neg (but taken at like 5 at night if that has any affect...i know ur supposed to do it inthe morning for best results...my bad.) I have noticed I am bloated lately, and I have been feeling like i am getting my period for like a month but it never comes...(like almost cramps but not as bad) I have had headaches and my breasts are kind of sore. not like unbearable or anything. I also get very tired, and sometimes dizzy. I can only be active for like 3 hours at a time and then I feel like taking a nap. I also am drinking water like CRAZY and can never satisfy my thirst. Any ideas? Could there be something else wrong with me? Any answers appreciated..