Do i have a chance of being pregnant?

Ok well I'm 21 I'm a mommy to a 6yrs old little boy. I've been trying to get pregnant for 2yrs now my period is irregular. I started my period on 6/01/11 lasted 12days, I got positive ovulation on 6/18/11 I had sex on 6/20/11 he did sperm in me now we're wondering if I got pregnant... we had a hard time doing it during fertile cause our son was home lol but he finally went to grandmas on the 20th then we went to work so we only did it once... could I've gotten pregnant? i sure hope so... but ima take a pregnancy test on july4th and ive been cramping ever since the 6/22/11