Cramping occasionally, 20 weeks..when to be concerned?

I am 20 weeks 3 days I had an appointment at 20 weeks 1 day. Everything with baby and myself was perfect. Measurements and all. This is my first pregnancy so I have no idea what's normal. I know in the beginning I cramped occasionally  as well and was told it was me stretching. Does the same still apply now? I called the nurse practitioner yesterday because it was on and off from 11 am to about 4 and she said to drink plenty fluids lay down and put my hand on my belly. If I was contracting more than 4 times in an hour to go in..but I don't know what a contraction is or if it's possible I am just have some Braxton hicks as I heard they can stay around this time now also. I know she said if my belly got hard, that was a contraction and more than 4. It stopped around 4 and I didn't cramp since.