Pregnancy Scare

So I had sex with a guy unprotected and he finished in me unfortunately. According to this app I am 8 days late but I never come on at the exact time the app says. I am on the implant and have been for a while now. I’m having cramps but no sign of my period also back pain. Could I be pregnant or is my period on the way? 🤷🏿‍♀️🤔