PREGNANCY SCARE- what do I do?!?!

I had protected sex with my boyfriend on New Year's eve. I was supposed to get my period a few days later, and I got it. I heard that if you have sex a few days before your period and get pregnant, you won't miss your upcoming period but you will miss the next one after. I was supposed to get my period today and still haven't gotten it. For some reason I've been extremely stressed about pregnancy, even though we used a condom (he did cum in me with the condom though). I've been really nauseous since Sunday and I normally never get nauseous so it's freaking me out. I sometimes feel like I'll gag too, but I haven't gagged or thrown up. I don't really have any other symptoms aside from feeling abnormally warm, and a little emotional/anxious. As far as I know there hasn't been any change in my breasts, no headaches/back pain, and I never had any implantation bleeding. I've been with my bf for three years but I'm a senior in HS going to college next year so obviously I can't have a baby right now. My friend was telling me to take a test, should I? I'm so stressed I could cry.