What Are The Chances Of Pregnancy Having Pregnancy Test Result Negative?

Hi, my name is Manuschka Brazier, I am a female and I am 18 years of age.
I had my period may 6, 2010, my boyfriend and I had unprotected sex may 7, 2010. On May 12 my period went off. Me and my boyfriend had unprotected sex May 26 and 28. I started having very light bleeding I would say may 24, sometime round that time and. My light bleeding had came to an end on June 15 but on June 16, my boyfriend and I had unprotected sex again and today June 17 this morning, I realized that the light bleeding came back but this time it was lighter then ever. I went to a clinic to take a pregnancy test around 5pm June 17 and it came out negative, but I have the strongest feeling that I am pregnant. Did I take the pregnancy test too early or should I go take a blood test instead? How long should I wait to take another test, or is there a possible chance that I'm just not pregnant. I would like to have a call asap please. If I can get a call tonight, I would be so happy because I am very worried.
Thank you