Hi, at 12 weeks my eldest was going through the night for 12/13 hours and had several sleeps for at least an hour at a time during the day. Wasn't quite as big as your baby, but definitely slept more when having a growth spurt. Was always a good sleeper, as were my other 2 dcs.
If you are worried, see if you can get a telephone appt with your GP, and mention it at baby check up appt.
Possibly grumpy as hungry when he wakes up? Have you checked his gums for teething?