when my kids where little I remember they had rectal itching and the doctor found pin worms, pin worms are very contagious because when you itch, the eggs get under your nails and then you touch something and then someone else touches that same thing and then eats.....spreading the eggs into the digestive tract. the mother will leave the digestive tract at night and come out through the anus and lay her eggs in the folds of the rectum which causes the itching. to diagnose, you can do 1 of two things, have your spouse (in this case) in the middle of the night check your rectum for the worm that has emerged (i know sounds gross, but parents would have to do it) or 2. in the morning before you wipe, take a peice of scotch tape and tap it to the rectum and place it on a jar or other peice of glass and take it to the lab your doctor wishes for testing. I think they have OTC pin worm treatment now, but I wont swear to that.
Sometimes you'll have itching if the anal area gets some waste on it... which in your case is this discharge you refer to. Just keep it clean when that happens, a damp tissue with a little plain KY jelly on it and wipe it off. Probably it's coming from a little constipation, which the waste will sit in there a little too long, and the body naturally wants to push it, and all that comes out is liquid. There's a lot of mucous associated with the bowels moving. Soooo, extra water daily and adding a little more fiber to your diet will help, and by fiber, just adding an extra couple slices of 100 percent whole wheat bread daily ought to take care of it, or more salads, or cheerios with a little juice in the mornings. Hope this helps.