In early july i had sex and i got a 2-3 day period immediately afterward but haven't had any periods since. could i be pregnant?

Possibly: Wise to get a pregnancy test to be sure

Possible: It is always possible to get pregnant after having sex which I assume you mean penetration of penis into vagina and discharge of sperrm in the vagina. The chances depend on many factors including time of the month, whether you take OCP's or other birth control, whether you use a condom, etc.