Growth Spurt?

I think Micah must have had a growth spurt recently. All of a sudden his 18 month clothes are too small! More specifically, it's the onesies. It looks like he's wearing 3/4 length sleeve shirts! And they are pulled pretty tight to snap them at the crotch. I suppose it's been happening over a period of time (he's been in 18 month size since mid summer), but it really seems to me like it just now happened out of nowhere! So I've been shopping for 24 month onesies and pants lately. Wouldn't you know, they're hard to find?! I think it's because many of the winter clothes are on clearance now, so they're picked over. I know I could look at 2T size too, but I think his body type is more of a 24 month (bigger in the middle and not as tall). He does still fit many of his 18 month pants, but most of the shirts and onesies are being rotated out. I can't believe how big he's getting! His next doctor checkup is in a month, so I guess I'll have to wait until then to see what he weighs and measures. That seems like forever!