I've never been backed up for several days, but I do feel at times like I have waste that needs to come out but it can't GET out. It is like there is a kink in there, or a gas pocket that has blocked traffic. I have found that sometimes sitting on the toilet and stretching upward and sometimes massaging my abdomen with small, firm circles can help get things moving.
If I am having 'trouble' it is not unusual to spend 10min or more sitting on the toilet to be sure everything has evacuated. I seem to only be able to eliminate in small portions when my stool is very loose and it takes about 10min for everything to travel out. Otherwise, I am up/down/back/forth on the pot because I didn't give everything time to evacuate. When stools are firmer, they are usually able to evacuate in one large sitting, though I will still sit for 5-10min to be sure I am done. I really HATE going to the bathroom, so I don't want to be gong back/forth and would rather get it all out at one sitting.
Anyway, try the stretching and deep massaging to stimulate your bowels to move, see if that helps.