emergency!

Ok I'm having a pregnancy scare at the moment. I'm already 4 days late of my period, and I had sex on my 21st day of my cycle, it wasn't on my fertility window period and I did have unprotected sex. We've done this before and I haven't been pregnant and in his past relationships he's used the withdrawal method and none of them got pregnant. I have taken 7 tests through these 4 days, 4 came as negative, 2 were duds and my 7th one had a very faint negative symbol, do I don't know if it's a dud or not. I'm worried that these tests aren't working and I don't have my own Medicare card and due to my heavily busy schedule with TAFE, work and other obligations I can't see a doctor. Thoughts? Anything I can do to trigger my period? Or another way I can test if I'm not pregnant?