I need of advice

Before anyone tells me that I should ask my doctor : I have an appointment for tomorrow morning :)

So here is my situation: I am 27w3d measuring 28w3d. I had really bad cramps for 5 hours on tuesday. My first guess was that I am constipated but I had very very soft stool.. then it was good for some days and today I have it again. Really bad cramping almost like a real bad period with a lot of lower back pain .. I drink so much water and relax a lot. Did someone experience something simular or has any advice if getting nervous would be appropriate?

Thanks in advance