According to this:
What's The Risk? - Five Easy Pregnancy Risk Assessment Flow Charts
...you have a very low risk of pregnancy. The negative test indicated that you are not pregnant; they're very reliable, really.
Stress can dely your period, you know, so it's very possibel that's what's going on here.
Good for you for using condoms and making sure you have access to a clinic. I think your visit will put your mind at rest, so let us know how it goes.
Hope this helps,