Periods with heavy cramps. Is required?

Hi doctors , On 22nd May I got pelvic scan report and it's showing simple large cyst of 4 cm. And also My menses was irregular and prolonged so my gynaec gave Primolut - N for 21 days so it ended on 15th June . Then I got periods yesterday on 17th June with heavy cramp and unbearable lower abdomen pain . I suffered whole night with pain today morning I took Meftol spas tab . So my pain reduced . And bleeding is normal . My query is why so much pain m having ? I never had such pain in my periods. Is this because of cyst or something else ? Do I need to take this tab continues when I feel pain I mean three times or two times a day . ??? Pls suggest . Or is there any chance that cyst raptured so feeling pain ?? What could be the reason pls suggest me doctors what to do ?? Shall I I visit to doctor ??? And when second scan is required ??? Pls answer my queries . Thanks in advance .