Uterus tightening. is it normal?

Znb • Ttc after MMC in May.
So since I was 15 weeks I started feeling this tightnening feeling in my uterus where my uterus becomes really hard for few seconds then it stops. I wasn't concerned in the beginning and thought it was just my uterus expanding. Now at 20 weeks I still get this but quite more often, like more than 8 in a day. I wouldn't say they are "painful" but they are so uncomfortable. Has anyone experienced that and went on to have a normal pregnancy? I'm afraid these are early contractions that may lead to a preterm or something. My appointment is in 2 days but I wanted to hear from other people's experiences. Btw I don't have a UTI and my last US at 14 weeks showed that I have a normal cervix length.