Cramping

So I got off birth control in late June. Have been having unprotected sex since august. Noticed my cycles were about 29-30 days instead of 28. Well this month I started a day earlier than I usually have been since getting off bc. My ovulation day or the day that has the highest chance of pregnancy was the 9th which we BD'd. On the 8th I had slight constant cramps and then today (3dpo) I'm getting them again. What could this be?