Hi pregpan
If he is uncomfortable then ring a midwife/Dr for their opinion but they will probably tell you that it is normal. W used to go every nappy change and now only goes a couple of times a week. He may have gas pains, try laying him with his nappy off and moving his legs in a bike-riding motion taking his thighs up to push on his belly a bit. We do this sometimes and it seems to get the farts out.
If W hasn't gone for a few days he can get a bit grumpy just before it happens, I think he gets a bit of tummy pain.
Hope he is o.k