What Causes Black Stringy Discharge While On Birth Control?

Im a 17 year old female and for the past 2 weeks ive been experiancing black stringy discharge. ive never had this before. its not enough to wear a tampon or pad (when i put a tampon in and a few hours later took it out i had a little amount of discharge on it and at the tip of the tampon it was like a layer of skin, but it was back). but its enough to stain my underwear and worry me. it keeps me from being sexually active with my boyfriend because it is just so disgusting. (and everytime we do the discharge comes out more lighter like a brownish-orange) i have been on yas birth control for the past 3 months. i hadnt had a period since december (ive been skipping my placebo(white) pills so i skip my period. but this is the first month that this dicharge has came out). ive had unprotected sex but never let my boyfriend ejaculate inside of me. im not pregnant. ive taken 4 home pregnancy tests and they are all negative. i have not shown any signs or symptoms of pregnancy. only the missed period. right now i am experiancing shocking pain in my pelvis area. i have a lower apetite than normal.

i am very worried. please help give an idea if i should be worried or not about this?