I think for some it just never goes away. I can empty myself completely with a pump, latch him on and as soon as I letdown, the "other" boob starts fountaining and has filled back up by the time DS is done with the side he's on. Around 10 (ish? don't remember exactly) mo DS started to prefer nursing while sitting upright on my lap and he stopped needing to burp so much during meals.
The most frustrating thing for you is probably the gas. I know everyone says 'belly to belly', but have you tried just sitting him up in your lap with an arm down his back for support and letting him turn his head toward you a little for a feed? Mine doesn't swallow nearly as much air when he's very upright.