Hi Amya,
Miriam has given you some good advice. I would just add that you might want to check out these two posts related to 4 month old sleep. One explains sleep for a 4 month old and the other talks about what kind of schedule works well for a 4 month old.
http://www.babysleepsite.com/h…..old-sleep/
http://www.babysleepsite.com/s…..-schedule/
I would definitely compare your schedule with the one Nicole recommends as a good day time schedule can help with night time sleep.
At this age, you can expect he will need 2-3 feedings every 3-6 hours, so what you're experiencing isn't uncommon. (That's not to say, it isn't exhausting!) But if you are getting 3, 4, or 6 hour blocks a night, that's actually pretty good. I would just offer that you also try to rest when he's napping during the day to avoid becoming overtired.
It's often tempting to try to get a bunch of stuff done while they nap during the day because this is your only free time. But really, some of that time, while they are this young, should be set aside for you to rest. If he's napping for 2 hours in the morning, then it may not be realistic to expect he's going to nap longer during his other day time naps. Two hours in the morning is a really good nap length and seems like that's what his body is saying he needs.
Hang in there! It sounds like you are on the right track. It's very likely as he gets older here in the next month or two, that you will see longer sleep stretches. Just try to avoid creating any sleep associations such as rocking to sleep during this time.