There are any number of reasons for a woman's periods to become irregular or stop altogether. Stress is certainly one of them. And stress can wreak havoc on the gastro-intestinal system, as well. But, everything presenting at the same time indicates that it may be something more complicated and time for a visit to the doctor, or her gynecologist if she has one. There are many issues/conditions related to a woman's reproductive health, including endometriosis, that can include one or all of these symptoms. Most are treatable and not a reason to panic. But, waiting and worrying until symptoms become worse can make diagnosis and treatment more difficult in the long run. Cudos to you for caring enough to check things out for your girlfriend! Now give her a hug and tell her to stop stressing and make an appointment. Hope all goes well.