Worried! Please help!

I’m 32 weeks and I’m scared I may be going into preterm labor. Ever since this morning I’ve had dull cramps in my lower back and it’s constant. Well about an hour ago my stomach started getting crampy as well. But it’s not coming and going, it’s constant. so I’m unsure if these are contractions since I’m a first time mom. I am also having a lot of pressure down there and also feel like I need to poop. So I have pressure in the front and back. I don’t have to poop though because I’ve had diarrhea all day long and I literally have nothing left in me (sorry tmi). Should I call my doctor or am I just overreacting? I’m only 18 so I’m super worried and scared and just don’t really know what to do.