i'll tell you something that works for me - freshly ground flax seed. I too have the problem of getting so constipated that an enema won't work. though as propaul suggested a soapsuds enema could work for you. it usually works for me when a plain salt water enema does not. but back to the flaxseed i grind two tbl of whole golden flax seed in my coffee grinder, put it in about 12 oz of water and drink it down. followed by another glass of water. I would definitely suggest to do the grinding yourself rather than to buy pre-ground flax seed. I would also suggest the soapsuds enema first to get cleared out and then do the flax seed daily to stay regular. i have suffered from chronic constipation for years (i.e. no urge to go like you) and flax seed never fails to work for me. give it a few days but i would be surprised if you don't get a healthy bm by the 1st or 2nd day. good luck!
also foods that i try to avoid even though i love them....rice and cheese...these are really constipating foods at least for me.