Google "four month sleep regression." Apparently, there is this phenomenon where babies' sleep patterns get worse at four months and at eight months. And, from what I read, it's much more common in boys. If you are on npn, there are a few past discussions on there as well.
In some cases, people can point to specific development happening (could this be the beginning of teething), but in other cases, it just happens. In my case, I went back to work when my son was four months old which compounded the situation.
There are different schools of thought about how to handle, but at four months, you have to feed them when they are hungry. I feel for you - it's really hard for the mom to go back to getting up at night when you've gotten used to sleeping through.
I think the same rules apply for working through this. Do all of the things that helped you get him sleeping through in the first place - make feedings as short as possible, don't change his diaper unless he's pooped, don't engage or make it "fun" to wake up.
He will work through it...