What Causes Periods And Pain In Ovary After Menopause?

had gallbladder surgery with my right ovary removed due to a soft ball size tumor growing on it in 2004.. I had went into menopause in 2011 and started estrogen med.. last week i had a period?? with enormous pain on my right side where my ovary used to be..? why did i have a period now its been 3 years and what could have causing the pain