What Causes Stomach Ache With Red/brown Discharge?

Hi, I had a strange stomach ache all day thursday and friday morning. I had noticed a few days before that i was sort of having a period with pale pink discharge which soon changed to red/brown gunk even though i haven't had a proper period for approximately 1 year as i had the mirina coil fitted over a year ago. By friday afternoon i had chronic diarrhoea which lasted in to saturday morning. The diarrhoea has subsided but i still feel quezy and still have a stomach ache and red/brown discharge. Is this related to the mirina or not having had a period in a year or an infection or a bug or something else completely? I am 37 years old, approx 5'9" and weigh 20 stone. Thanks.