Late period

Im starting to really freak out. I usually get my period on time and this time I didn’t, I was supposed to already start it and i didn’t. I had unprotected sex 8 days ago and can’t help but think I might be pregnant. I took a pregnancy test and it came out negative. Lately I’ve been feeling really tired, low appetite, and super nauseous. I’ve been having some period symptoms but then I can’t help but think they might be pregnancy symptoms. I’m not on any birth control and didn’t take a plan b since I didn’t think I could get pregnant just before my period. I’m freaking out because I honestly don’t want to be pregnant. I’m too young to have a baby right now. Should I be worried?!