What can I do? Any ideas?

My son is 3 months old. He hardly sleeps for more than 1-2 hrs at a time. Every once in a blue moon he will sleep 3-4hrs. He eats formula with rice cereal because the doctor suggested it because of his reflux problems. He eats 2.5-6 oz in a feeding sometimes more but he tends to fall asleep when I feed him and then wakes up very soon after to eat again. He also refuses to sleep laying down in his crib. He sleeps in his swing or next to me and I have to prop him up because he wont sleep flat. He is and always has been a lil congested so maybe thats why he cant sleep flat but Im getting exhausted and I dunno what to do. Any ideas of what I can do to get him to sleep longer and sleep on his own??? thanks