Pregnancy tests are pretty accurate, especially since you took yours so late (the 9th day of a missed period). You can take another in a week or so, if your period hasn't come yet, and if it's negative, be sure you aren't pregnant.
On the possible yeast infection: The symptoms of a yeast infection can be like those of many other conditions/STIs. BEFORE you treat yourself, you need to make sure that what you have is in fact a yeast infection. If you treat it yourself with OTC stuff and you don't have a yeast infection, you could wind up with one.
Also, if you've had a pregnancy risk, you've also had an STD/STI transmission risk. So right now, first priority needs to be scraping it together to see a doctor and get an STD/STI screening.
Some Planned Parenthood locations offer services free or at a reduced cost. Check out this for services in your area:
"And when the answer that you want/Is in the question that you state/Come what may..." - Coheed and Cambria, "Blood Red Summer"