Arthrotec is the brand name of a combination product that contains two medicines: diclofenac (an NSAID) and misoprostol (to protect the inner lining of stomach). It is known that diclofenac when given for very long duration can hurt the stomach, but it has no effect on uterus or menstrual cycle. Apparently your earlier-than-expected bleeding was not connected with the intake of Arthrotec.