For the last... oh, more than two weeks now I think, Alex has been wanting to feed every 1.5 hours during the day

I can usually stretch it out to 2 hours but he gets pretty grumpy about it. At night he'll do 4-5 hours.
It used to be that he'd easily do 3 hourly during the day and 6-8 hours at night.
What's gone wrong?

Surely no growth spurt can last this long?