I haven't eaten in 3 days, but I have absolutely no appetite...This seems to happen sporadically... What could be wrong with me?

Could be many things. This is not normal and could mean you have any number of things. You definitely need to see someone and get your abdomen examined and some blood tests to see if it is serious. Stop drinking alcohol (if you are) and force yourself to drink lots of liquids even if you are not thirsty, and try to get some protein in small quantities throughout the day (egg, cheese, nuts, tofu, yogurt).