Stopping/starting bc; late period; neg home/blood preg tests

I had a period in the 2nd week of June and was supposed to start my new pack of bc at the end of the week, I didn't. I also wasn't sexually active. I got a period in the 1st week of July and I started a new pack at either the end of that week or after I finished. I was sexually active during then into now. I'm into August and have not had a period but 2 negative home pregnancy tests and a negative blood test.I really don't know when my period is supposed to start now but...Did I just throw my period off or am I pregnant with not enough HCG to detect? Should I expect it next month?