Hi C.,
First I'll start off saying that my oldest son, now 10, wore pull ups at night until he was 4 1/2, my middle son, who is now 7 just started (a week ago) going all night without wetting. My 5 year old daugter still wears pull ups at night. She is dry about 50% of the time.
What I suggest is that you either let this go awhile longer or you can opt to get up once or twice (depending on what is needed) to put your son on the potty. I still put my 7 year old on once at about 10:30 and then he goes the rest of the night dry. We also learned that we had to cut off liquids by 6:00 pm in order for him to be able to stay dry at night. He goes to bed at 8:30. When we put our daughter on the potty during the night she is so tired that she isn't aware that she is on the potty, so she doesn't go. They are all different and do things in differently, so you kind of have to see what works for you all.
Do know that this is very normal and your son is still very young! A friends daughter didn't get out of pull ups until she was 11. They tried everything they could, but it happened when she was ready!
Good luck and take care!