My daughters doing the same one week she'll be like a week a head then 2 weeks later I'll go in have gained like 5 lbs and shes like 3 weeks ahead and is been that way for a few months now and im 31+3
Well I hope its not another growth spurt lol he's been measuring and weighing 3 weeks head since 15 weeks !
Don't worry hun it's normal. I go through that like every other week lol it all depends on when baby is going through a growth spurt or where their sitting