Pressure&cramps

I’m currently 21+4....since a few days ago I have been experiencing tightening in my abdomen along with hip cramps. This is my second baby and felt exactly like contractions. Today I have a lot of vaginal and rectal pressure where it feels like a bowling ball is in my pelvis ready to fall out. I did see my dr yesterday on May 6 and she gave me a trans vaginal ultrasound. The dr told me my cervix measured 3 inches long but April 22 I had my anatomy scan and my report said my cervix was 4 inches long. I am worried I am going to have a preteen labor or something is going on. Has any other ladies had something like this happen to them??