Visit a City of Houston STD clinic at either the Medical Center location on Braeswood close to Ben Taub Hospital or the West End clinic near Heights Blvd and I-10. Unless they've changed the prices, for around $10.00 you may be tested for gonorrhea, chlamydia, syphilis and HIV. I'm sure there are other tests that can be performed as well, probably for a nominal extra fee. Services offered include counseling education and more. Assuming, of course, you reside in Houston.