What Causes Irregular Bleeding?

have irregular periods (once a year unless im on birth control) and ive been having them since i was in high school im atheltic. Well recently ive been spotting like old dark blood its not heavy its just when i use there bathroom. Its been going on for two weeks now. I have cramps but im not bleeding just spotting and my lower back has been hurting and this week my nipples have been sore. Im also a clear gel like substance is coming from my vigina. What could be going on