What to do if you have bad abdominal cramping and diarrhea during pregnancy
If you have any concerns about the health of your baby it is always best to call your doctor for advice.
Otherwise, it sounds like a GI issue. It might be a virus or food poisoning. I suggest making sure you are drinking plenty of clear fluids to stay hydrated. Also try eating bland foods that won't irritate your stomach. Try the BRAT diet, bananas, rice, apple sauce and toast.
I would also consider cutting dairy out of your diet. Some women will develop lactose intolerance during their pregnancy. Lactose intolerance causes horrible stomach cramps and diarrhea.
If you become dehydrated make sure you go to the doctor. If your symptoms get worse or don't improve after a day you should seek medical treatment.