How do I know if I'm going into early labor?

I am 34 weeks pregnant, I have a ureteral stent and I've been having bad pain in my lower abdomen, Saturday it would come every 20 mins and last for about 10 mins, then got to where it was almost constant, but since then it hasn't been regular. I'm going to the doctor tomorrow, but I want to have a general idea since it's at least an hour drive to the hospital, and a four hour drive to the one I would prefer to deliver at. (After 36 weeks I'll be staying closer btw) Anyways, I'm so used to my kidney/bladder hurting I don't want to wait to long and not make it to the hospital because I missed the signs. People have told me contractions feel like the baby is balling up and your stomach gets hard, but that has been happening daily since 16 weeks or earlier, so that's nothing new. What do contractions feel like when you already have pain in the kidney area?? I've been having more watery discharge, but that's the only new thing besides this different pain. I know this is all jumbled so I'm sorry lol! Thanks for any advice.