I am currently going through the same thing. Some ideas that have helped in the past are listed below. Like most of you, I've also consulted my doc about it and the things I found that seem to help are:
1. A good diet plan at least a week before-(i.e. no greasy foods, no dairy products, no candy/chocolate, no carbonated beverages/drinks, no sweet treats.
- Instead eat plenty of fresh fruits & vegetables
-Decrease meat intakes; try only eating fish during this time
-Take/eat ginger...there is a tablet/pill form of it you can get over the counter... a week before your menstrual starts (helps with digestion); or take some type of antacids.
-Take pain pills a week before your menstrual starts (ex. some pain pills may not help...Aleve is the only thing that helps me. Midol makes me cramp more.You have to find what works best for your body.)
-Make sure to drink plenty of water during this time and green tea (drink this at night)
-Hopefully everyone is already taking vitamins daily.
-If you are not already, start exercising at least a week before.
-Something new I started was taking Vitamin D (you may want to consult your doctor about this)...
Remember your body is losing blood/nutrients that it needs; so it is important to replace these things.
This is everything that I do to decrease the cramps, vomiting, and diarrhea during my period.
Best of luck...