Contractions during anatomy scan?

I am 21w and 2d, I had my anatomy scan today and it took them 2 hours to get all the measurements, they kept having to stop for 30-40 seconds at a time to wait for contractions to pass, it happened during the whole scan. I got home and took a nap because I was really tired, well when I woke up I noticed horrible pain in my pelvic bone. It hurts so bad I could cry! I cant even lift my leg due to the pain, is this normal? This is baby 3 and I have never dealt with this. Has this happened to anyone else, if so what was the cause ? I'll be calling the midwife in the morning if it doesnt stop or gets worse