help please

Maddi
I had (protected, he wore a condom and he came but he said it didn't break) sex on the 20th day of my cycle. And my fertility window ended on the 18th day. It's now the 31st day of my cycle and the app says I should start today. I have really tender breasts and some cramping but my period hasn't come? I'm only 17 and I don't know what to do.