Believe it or not, the VAST majority of boobie-feeding moms only feed one side per nursing. My guess is that your milk supply is perfectly matched to your son at this point, so he gets a full feeding on one breast. A 2 hour gap IS the norm for a 3 month old breastfeeding baby because the milk is digested so quickly and their tummy is still tiny.
And, I suspect he is coming up on a growth spurt, which means he is going to eat more often. Remember - he can't make his tummy any bigger, so he just nurses more often.
As for sleeping through the night - HA! In all my years counseling breastfeeding moms and running breastfeeding groups, I have never heard of a 3 month old breastfed baby sleeping through the night. Actually, most get up at least once a night to have a quick "boobie bar" all the way until they are 2 years old.
They best thing to do for sleep is co-sleep. I have co-slept with all my kids and it saved my sanity - you just roll over and whip it out. Before you know it, within 5 minutes they are back to sleep and so are you.
Great job with the baby and tatas!
:)