You can be dilated for many weeks. However being dilated at 31 weeks is premature and you should be treated as a possible pre-term labor risk. Dehydration causes contractions so when you feel crampy and feel those contractions put your feet up and chug water!
I would just take it really easy and discuss your concerns with your doctor.
Dilation isnt accurate to determine labor. Ive been 2 cm 60% effaced and at a -1 station since 32 weeks im now 38 1/2 weeks and have only dilated 1 more cm. Ive gotten contractions almost all my pregnancy as well. Like degriffdog said if you get 10 in one hour than go in or if you are concerned ask your doctor.
If you are having more than 10 contractions in a hour than you need to be seen. I had a lot of braxton hicks contractions with my 3rd for most of my pregnancy. You can always call L & D and ask them what they think.