My girlfriend missed her period sunday and still didn't get it. Every morning she wakes up with bad belly pain. What could this be?

Home pregnancy test. The most important thing is to determine if she is pregnant or not. Buy a home test. If positive then she needs to be soon as pain in early pregnancy is a red flag for a medical emergency called an ectopic pregnancy. If she is not pregnant and her periods are abnormal she should schedule a visit with her obgyn.