Pregnant?

I'm 15, actively on birth control, currently sick. December 9th, I had protected sex with my boyfriend. December 11th, we had unprotected sex. I got really paranoid because I had just gotten off my period of two weeks on the 9th and research says the likelihood of pregnancy is slim but still possible. Since I was late ordering my new pack of birth control, I was not on birth control. 
We had unprotected sex again, and that time, he was extremely paranoid so I took a Plan B pill. I didn't receive any side effects, and I continued to take the new pack of birth control. However, whenever I got my new pack, I also got amoxicillin for strep. So my bc is less effective. 
It's December 27th, I'm nauseous, I have an upper respiratory infection, and my period is late by three days now. I've been trying to get a family member to buy me a pregnancy test, but she's a little butthurt since it's so hard for her to get pregnant. 
What should I do?