M.S.
You know your body the best, so definitely get a 3rd opinion, so to speak. I went through the same thing....my periods were always regular, and I always got signs right before I started. The time I didn't, even after using BC, I took a test and it was neg. So, I had to go to my gyno and, sure enough, I was pregnant. So, just call up your dr. and you will know for sure. Everyone is different, so your levels may not be detectable right off the bat for a postive.