Brill, just to eliminate reflux, why not prop up his mattress at a low angle. Roll up some towels and put underneath head area so that he's 'slightly' elevated. May help. If you can, try and wear him in a sling (wraps are v comfy for you and baby) so that he's upright a lot of the day. You'll probably get more done whilst he's in the sling.
BUT, BUT, BUT.... green poo in breastfed babies is a sure sign that they are getting too much foremilk, regardless of his weight gain, and that he's not getting to the richer hindmilk. Too much foremilk will also cause colic......
Hindmilk is high in calories and ensures that your baby feels fuller, for longer. If he's not getting this, then, in addition to the colic he's getting from the sugery foremilk, he's also getting hungry extremely quickly and will need to feed more often. Sound familiar?
Too much foremilk will make him have runnier, green poo and the increased gas in his belly (from the too much lactose) will give him cramps.
Any chance you can tell me EXACTLY what your feeding routine is? I may pick something up....