You most likely are not pregnant. Even though your periods are irregular the chances of you ovulating during your menstrual ccle are very low. I would wait to take a test until atleast May 25th but again the chances are pretty low.
More than likel you are not pregnant. It IS possible, albeit very rare, for a woman to ovulate very early in her cycle and become pregnant during or right after her period. As I said this is rare. The best thing to give you some peace of mind would be to either wait 2 weeks from the last time you had intercourse and take a test or to be even more sure, wait until your next period is due and see if it shows up on time.
If you had sex during your period than you wouldn't be pregnant. Typically women ovulate around the 14th day of their cycle. The first day of your period is the first day of your cycle. So you would have to have unprotected sex around the time of ovulation in order to get pregnant. Sounds like to me if you have a cold, you probably have drainage running down the back of your throat and into your stomach making you sick. I really seriously dought with you having had sex on the 1st, 2nd, and 3rd day of your cycle that you are pregnant. I hope that this helpful. :)