What Causes Throbbing Pain In Lower Right Side Of Abdomen?

my question this sensational feeling of like a throbbing only once in a while in the lower right side of my abdomen at the right side of the pelvic area it is not painful but it is throbbing. when I exercise at the gym I bleed with a very red color but it will stop, even if I only do 20 min brisk walking what is the cause of this?