What Can Cause Sudden Infertility?

hi lm 29 years old had a miscarriage when l was 22 it was a twin pregnancy, got pregnant 4 months after that and have a healthy 7 yr old son, l used depo when my so was born and stopped when he was 2, l had continous mensies thereafter and had to get onto oral contraceptives to stop the bleeding. a year ago l started trying to get pregnant again and am failing to get pregnant, lm still with the same partner not using any contraceptives and had full blood picture done my hormone levels are ok, l have 25 day cycle . my period was a 2-3 day cycle till this month it went back to 5 days after 5 years. what could be the cause of my sudden infertility? have been feeling abdominal movement on the left side but just had a full on period.