What Causes Irregularities In Periods?

Hello doctor, I have irregular period for last 2 -3 months , and I gain to much weight also , I go to the doctor and she give me krimson 35 , I am 32 years old now , is the medicine really helpful , is any side effect of this medicine , because me & my husband planning to make a baby after 2 years ....... Is I facing any type of problem to take its medicine pl help