Am I overreacting?

I didn’t have a period in may then I had one from june 8-12th and then I was supposed to have one around the beginning to middle of July, but I didn’t. I had unprotected sex on July 12th. My prediction is if I had a period I would’ve started ovulation on July 15th. Is it even possible for me to be pregnant and if it is how far along would I be? (I did not have sex in may or anytime before may) I’m 16 but would give birth at 17 if pregnant and I don’t want to buy a test or go to a doctor yet until I know there’s a big chance im not overreacting.