Hello girls, can anyone tell me? I'm experiencing something like I fee…

Hello girls, can anyone tell me? I'm experiencing something like I feel my uterus right at the bottom of my abdomen, there's a feeling that it's tightening there, from the bottom of my belly to the side, and even kind of radiating into my hip area, what is this? It doesn't hurt, but I feel like I feel the uterus itself and the tension, I don't understand. Ultrasound was done last week, everything's fine they said, but I still can't stop worrying.