Loula, this can happen at times and is probably fine - except it might mean some extra feeds in the night! Babies at that age generally need 8 or more feeds in 24 hours, so it would be a good idea to keep an eye on his nappies and make sure he is still having plenty of wet and dirty nappies. If the nappies slow down then you might need to wake him every 2 - 3 hours for a feed. Most of the time the adage "don't wake a sleeping baby" is a good one, but there are times when you need to.