My name is Jasmine and I am 21 years old. I have been having an accelerated heart rate for no reason. I could be sitting down and it starts racing. I was told it could be a sign of being pregnant but I brushed it off seeing I have not conceived since I've been with my partner. They asked when my period should be here and I then realized it should have been there that day (7/18/08) it actually didnt come til the the 20th. The conceren I have was that it was not like my regular period, it was dark and lighter than my usual period is. I lasted just about the same length of my period 6-7 days. I took 2 hpts but both came out negative. Should I be worried?