Is something wrong with me?

Im scared because i haven't had my period this month and i was wondering if somethings wrong with me. I haven't had sex for a few months and we were safe about it, and every month i have had my period after i had sex so im pretty sure im not pregnant. But Im wondering if it could be stress or my new diet, Im extremely stressed out because Im about to start college and I have to find a job asap! So Ive been freaking out about that. And I also recently became a pescatarian, it means i have stopped eating all meat except for fish. So could that have changed my cycle? Please help im really scared and I dont know what to do.