I need Advice.

I really don’t know how to start this. But I could really use some guidance. I’m 17 almost 18 years old. Yes, my Fíance and I occasionally have sex, but it is always protected as highly as we can. I am not on birth control. Just recently I’ve noticed that my period is late and seems to not be on its way. My mom asked if there was anyway I could be pregnant and I said I didn’t think so. As soon to be mothers or those who are already mothers. Could you give me some advice or anything. I’m scared and I’m not sure what to do. My period is officially 10 days late.