E.A.
You have a variety of things going on here. First, you can't shorten the feeding, he will eat until he is full. If he is wetting enough diapers, isn't gassy or uncomfortable after eating (more than is normal), he is eating enough. Make sure he is getting a long feeding on the first breast you offer, he needs the hindmilk. If you switch off too soon, he will not get all the fat he needs, which is what the hindmilk is full of. He will give you cues as to when he needs to switch, often they will pop on and off the breast because the flow has slowed down. But each baby is different.
Will he eat more efficiently as he gets older? Yes, but there will times when he will cluster feed right before a growth spurt, and It's similar to what you are dealing with now. I did find that increasing the number of feedings during the day will often allow them to eat more infrequently at night, but I fed on demand for at least the first 10 months, so I'm no expert at how to get them to sleep longer at night, that wasn't a priority for us.
Second, stop giving him formula unless you are trying to get him used to it for when you are at work. You are sabotaging your milk supply. In order to keep your supply up while giving formula you need to pump for every feeding you are missing. If he is spitting up the formula, and there seems to be a lot of it, you may need to switch brands.
Stop keeping track of the night time feedings. Why isn't your husband changing the diapers? That was our deal, at least for the first 4-6 weeks, he changed diapers in the middle of the night and I fed the baby. You are still healing from the birth, you need rest, or you will find yourself with mastitis.
You said, "I'm finding that I can't do much other than feed him day or night." And I'm here to tell you, that is completely normal for his age. That's pretty much all you should be doing. I don't know one mother who didn't say this during the first 6 weeks at some point. It's ok, no one should expect you to do much else right now except take care of yourself and the baby. I see in your profile that you also have a 4yo? Kids are great helpers at that age!