Am I just worrying or could I be pregnant?

The last time I even fooled around/had was at the end of May. I had a normal (but only 3 days) period in June and July, (at the beginning of each month like they are supposed to). But now I'm having another period right now? 2 weeks after my normal one in July?? It is very spotty and mostly brown discharge. I don't even use an entire pad in a day. What is this?? I have worried about being pregnant for a while now, so I have taken many pregnancy tests which all came out negative. If I were to be pregnant I would be close to 10 weeks- if i take another pregnancy test will it be correct? Does the test HAVE TO BE POSITIVE if I am pregnant this far? Or could it still be a false negative??!