What Causes Pain And Severe Cramps In The Abdominal Area During Pregnancy?

I am 5 months pregnant and having severe cramping it s as though I can feel my bowels move to my intestines and it s excruciating to the point where I double over. At first I thought I was constipated so I started eating prunes to help with that.. The pain has been going on for over a month now and it takes my breath away.along with the bad cramping ihave gas and it is hard for me to push it out. I also have pain from my belly Button all the way down to my rectum. I drink about a gallon of water a day. My doctor won t help figure out what s causing the pain. Any suggestions?