What Causes Right Sided Abdominal Pain When Suffering From Uterine Fibroids?

I have been diagnosed with several large fibroids, 1 at 10cm. I experience severe pain on my right side on the 1st and 2nd day of my period. I have just started to get dark brown discharge about 10 days after period. Could this be from the fibroids? I am 49yrs old.