Welcome to HCM,
Usually there are no chances of pregnancy
due to unprotected sex on last day of menstrual period, but in your case first day of period was 1st April, thus 6th April can not be taken as last day of period. As you ovulated 4 days after 6th April and using withdrawal method, chances of pregnancy are rare. How you confirmed date of ovulation ? Are you using Ovulation Prediction
Kit ? In a regular menstrual cycle of 28 days, ovulation generally occurs on 14th day of period. Stomach pains can occur due to so many other reasons. To remove anxiety
, it will be better to get simple pregnancy test done. Avoid unprotected sex in future, which will protect from disease transfer also.
Wish you good health,