Based on your LMP and a 28-day cycle (which is average), your fertility window may have been between February 6th and February 16th. While the second encounter definitely falls within the fertility window, I can't rule out the first encounter. Sperm can live inside of a woman for a few days and meet the egg when she ovulates. It all depends on when ovulation occurs. For most women, it is around the 14th day of the cycle, but that isn't a definite. Unless you took an ovulation test to see exactly when you ovulated there's no way to guess. Unfortunately, I suggest you speak with your doctor about a paternity test.