Hi Heather,
My daughter is on a 4 hour feeding schedule and is EBF. I know that when she sucks and spits out my breast that she has a burp in there. I don't know if that is the case with your little one.
Sometimes when Arwyn seems very hungry, I will move up to 3.5 hours and feed her. Most of the time, I can keep her distracted until 4 hours.
If you want to try moving to 4 hours, try to start on the weekend when someone can help you. My husband keeps Arwyn occupied and happy in order to stretch her feeding time to 4 hours but I can't be in the room or Arwyn becomes all whine-y once she sees me.
More milk please!
Depending on when your little one eats last, pump about 3 hours later and see what you get. If that is your regular schedule, your body should have no problem making some more for the "extra" feeding. It may take a few days to establish that.
Also, you could try to pump in between feedings for a short time. I noticed that your DS nurses very quickly... you could try to pump for half the time he normally nurses in between feedings. This will also increase your milk supply.
Last, if you feel your son is not getting enough milk and you want to produce more milk, you can see your doctor about taking Motilium (Domperidone) to increase your milk supply. I was on Domperidone for the first 8 weeks of Arwyn's life so that she could breastfeed as my body could not produce milk on its own due to blood loss during my C-section. You don't have to be on this for long, once my milk supply was established, I weaned off and now my body just produces what Arwyn needs.
Good luck Heather.