Jen,
I went through a similar situation several years ago (except it had been almost 2 months since my last period in my case. My cycle tended to be irregular, but that was worrying me.) I had a negative pregnancy test but was still not convinced and still scared. I saw a doctor at the health center who confirmed that I wasn’t pregnant. My period started a few days later.
Home pregnancy tests are usually fairly accurate. If you have taken 5 tests after you missed your period I would bet that you are not pregnant. I have heard of women who have a very very low level of HCG which isn’t detected through urine tests and the pregnancy could only be determined by doing a blood test. I wouldn’t stress too much, but if you are worried you could see a doctor to have a blood test or to determine if there are other reasons why your cycle is delayed. Good luck.
Kate