contractions

DS
First time mom here, can someone pleas explain how contractions feel?! I'm 34 weeks and starting two weeks ago I've had to have non stress tests done at the hospital twice a week because of a slight complication... anyways, everytime im there the nurse will come back in and ask me if I'm doing okay cause the monitors show I'm having contractions. They showed me on the chart a couple of times and some are mild, but then there are usually a few big ones. I haven't felt a single one!!