He's goin through a major growth spurt lol
Babies go through growth spurts at this stage a LOT too, the pain you're feeling is probably your baby going through a growth spurt. My little girl was measuring a week ahead at my 18w ultrasound, and then last week my 34 week ultrasound she was measuring 6lbs 4 ozs already, so she's going to be a bigger girl, too!! Just a big healthy baby! :)
Lol I'm 20+2 and my baby is only measuring 3 days ahead. They were surprised because I'm over weight lol
Glad it was nothing serious:)