36 weeks contractions??

Went to the Dr today I've lost a little weight....but my appetite has slowed down this last month. He did blood work since I'm throwing up again and I have protein in my urine. While measuring my belly he said I was having a contraction which I didn't think anything of just thought it was pain. He did some swan test not sure what it was for smh. Anyways how do u know you are having contractions? I'm not a first time mom but I didn't have contractions 9 years ago I had an emergency csection. I've had pain where its in my stomach to my back and down my thigh is that a contraction or braxton hicks?