He may have eaten something that has upset his GI track. Try feeding him some Rice and Boiled Chicken (or Boiled Hamburger Meat) - You need to give his system a rest. He may also need some probiotics (plain low fat organic yogurt) to replensih the good bacteria in his system, since he had a parasite and was on antib's
P.S. That is not his anal glads and it's not normal for this to happen often.