Hi, Actually My Periods Comes On Time ...some Time It

Hi,
Actually my periods comes on time ...some time it can delay but the problem is with the flow and the pain. 2nd day the pain is very high and the pain is unbearable till 3rd n 4th day. so, i went to Gynecologist she suggested me to take Duoluton-L for 21 days but i am scared of taking this pill
I want to know if it will have some side effects .