T.H.
My childrens doctor always told me that a breast feeding baby hardly ever gets air in their tummy so the burping can be hard. I hardly ever got a burp from any of my children. If the child has a secure enouch latch onto mom then the baby should be okay. That is what was always told to me. I then used the playtex bottles with my youngest and still then never really got a burp out of her. I always rubbed my girls back just to relax them even more. If your son does not burp honey let him sleep. If you feel worried about this then ask your sons doctor. That is what I ended up doing because with my first child I was affraid that I was doing something wrong. It is always comforting to know what the Doc has to say though.
Good Luck