16 and I have not had a period this month.

I have not had a period this month. I had unprotected sex on the 16 of august 2011 and my boyfriend said he came inside me little tiny bit when he was pulling out. I have been cramps on and off in my lower front and my sides. My boobs are swollen but thats all the symptoms i have, no period, cramping on and off and boobs swollen. I took 3 prego test in the past 2 weeks and negative. AM i testing to early or what you think, am i prego or no? PLEASE HELP, dont wnat to tell my parents unless i really find out i am prego. Thanks Rose