Hi,
Welcome to ehealthforum,
Based on your due date 04/13/2011 (40 weeks gestation), your probable conception date would be between July 15th to July 25th, 2010. If there was a period in between your two different intercourses, then the person with whom you had intercourse after periods would be the father. Since there is no period in between, it is difficult to comment on who the father will be. For accurate results, a Paternity test should be done.
Take care.