I would like to do a std/sti check. is this something my gp can do? will it be covered by my medical aid? if not how much will it cost?

Hard to say: This is the HT public site based in the USA where volunteer docs answer health questions. You are welcome to post such questions. However,we have no access to or information about the who,what or where medical facilities are, how your insurance works or costs in locations around the world where this site is viewed. Contact a local clinic for such questions.

Yes: Your primary care doctor including GP can easily run STI/STD screening and the cost of these screening tests should be covered by state-funded program such as medicaid. You may also check with your county health dept.