Tell that I have a STD from a test for cystitis?

Usually not. Most stds will not show up on a urinalysis or urine culture. It is now possible to test for certain stds (gonorrhea, chlamydia) with a urine test, but that is a different test, and the doctor would have to order it separately from the lab. Best to discuss all your symptoms and concerns with the doctor first, so that all of the necessary testing can be ordered.