I agree that you should get him checked out JIC. DD does this sometimes. I'll get a few days of grumy behaviour and masses of / no (depending, but always a huge change from the normal) sleep and then a tooth appears or a cold comes on or something - it's always for a reason, but not always clear for a few days what the reason IS iykwim.

Getting him checked out can't hurt though if he has formula it's pretty unlikely his iron is low. Not impossible (especially after a growth spurt) but unlikely.

Bx