Has your LO's routine changed any or has he been ill? My LO is 3 1/2 and had been dry through the night for a year when she started wetting the bed for about a week constantly. I think it was because she had a urine infection and was coming down with the cold.
We always made sure that we didnt scold her about it and told her it was an accident. Does LO get in bed with you after or do you strip his sheets at the time?
We kept a spare pair of sheets in LO's room with a pair of PJs so if anything did happen, we could quickly change her and put her straight back to sleep.
It could be that he just wants attention at night time when he is supposed to be sleeping and wetting the bed is one way of getting mum and dad to come through?
I'm really not sure hun but if you are worried i would take him to your GP for a check up. Otherwise, i would just ride through it and hope it is just a stage he is going through.