What Causes Reddish/purple Blood During Periods?

My girlfriend is experiencing small amounts of reddish-purple blood during her period. She says it has never happened ON her period, it usually happens beforehand. We have had sex, and there is a risk factor involved with that, I know. She is still experiencing stomach cramps and premenstrual syndrome qualms, like always, but with a lot less blood. The period also consists of old blood (brown) and contains basically zero fresh blood. She has always had trouble with periods, and consistently experiences migraine auras, is constantly drowsy, eats very little and drinks very little, which leads me to believe high blood pressure or some form of diabetes is involved. Due to these symptoms occurring prior to us having sex, it is hard to isolate them as a symptom of pregnancy. She regularly experiences leg cramps, and occasionally has strange "super" migraine auras wherein she cannot see anything and cannot feel her body. She's been referred to many doctors, but none could find anything wrong with her (at one point she lost feeling in her foot for a week, and all results returned negative). Could I get some help with this issue and possibly a diagnosis? I know it's a mixed bag of symptoms, and I had incredible trouble attempting to diagnose it myself.