am I overthinking

So my period was supposed to start a week ago and it hasn't shown up yet. We had sex once since my last period but I wasn't ovulating, we used a condom and he didn't finish inside of me. I'm worried and not worried all at the same time. We haven't really had sex that much since September. I work out on and off every so often and my diet tend to change depending on if I'm working out or not. I've also been slightly stressed with school.  Should I be worried or not?