When to call dr!?

For the past few days I've been cramping really bad and a lot of pressure in my pelvis. Today my contractions were consistent for 2 hrs then were not consistent so I let it go. About 2 hrs ago I started having contractions that were painful and went to my back. Then stopped now I have the pressure like I have to poop (which I did and had contractions during) and not just pressure and cramping. My son has his first school picnic & I don't wanna miss it for a false alarm but don't know what's going on and if I should worry. 😔