Yes it's very common. It depends on your baby's growth. First time i went to the Dr my due date was 14th June according to scan. But 8 according to my dates. On second scan it went to the 9th. Now the last time the scan says 5th June! If there's a growth spurt it also happens.
Yes i think your baby is growing quickly now
When i was pregnant with my first, I met another couple whose due date kept changing. I thought it was strange. I'm now pregnant with my second baby and they changed my due date based on the size of the baby. I never thought the due date could change either but yes, apparently it is common.
Mine went the other way I thought I was due 12 June then they changed it to the 22 now im back at the 12 of June.
It's so confusing why they do it but you baby must be mesureing a week ahead witch means baby is growing well xx