Thanks for the query.
1.The factors which delay the transport of the ovum through the tube can cause ectopic pregnancy
It can be congenital or acquired.
2.The chance of recurrence is 15% after first ectopic pregnancy.
3.Better to wait for 3 months.
4.It is not common, if the pain is severe better to consult your doctor once.
For more details:http://srsree.blogspot.in/2012/02/ectopic-pregnancy-types-diagnosis-and.html