How to know your in labor with contractions?

So I have high fluid in my belly and have been having contractions since about 28 weeks. I went into the hospital a few weeks ago because I was having 5 an hour and my OB told me to go in because I’m at risk for preterm labor. But my contractions weren’t bad, just uncomfortable and had some pressure. I wasn’t dilated at all. I’m now 35 1/2 weeks and I feel like a lot more lately I’ve been having what feel like SUPER heavy cramps, sometimes they wake me up in the middle of the night.

They never seem to last though, today my belly has been hurting like cramping again, and almost like I have to go to the bathroom/throw up, and I felt shakey. Not sure if this is normal? This is my second but I never went into labor with my first, so I’m unsure of what signs to look for to go to the hospital when the time comes. I feel like I have a high pain tolerance so any advice please???