HI. I Got Married 10th Of March. I Started Having

HI. I got married 10th of march. i started having primolut on 20th feb and had it till 21st march. Then my periods started on 24th march. usually my periods last for 4 days and first 2 days of heavy bleeding. but this time first two days of my periods are very less bleeding (like in the ending days of usual periods) and i noticed a 3 inch long,very thin, slice of a muscle or a tissue like thing this time. and starting of my periods this time was very painful than normal cycles. so what i wanted to know is, reasons for these changes. thank you.