Hello. Thanks for writing to us at healtharemagic Unprotected sex is always a high risk in terms of STD s. Ejaculation or not, has no significance. Some STD s may present shortly after encounter e.g gonorrhea, chlamydia, herpes etc. Others like syphilis may present later (incubation period is 3 weeks on an average). Warts and molluscum may remain clinically silent for months before one notices them. Moreover screening test for HIV (Rapid test) is usually performed earliest at 1 month, before that it is can be false negative. Therefore, testing at 18 days is not sufficient to exclude all of them. It can of course rule out or confirm herpes, gonorrhea and chlamydia. I would suggest testing for HIV and Syphilis (VDRL) at 1 month and then again at 3 months. In addition to testing if you notice any vaginal discharge, burning sensation on passing urine, genital ulcers/erosions, warts or growths or inguinal swelling etc you must immediately get it checked with a sexual health specialist. Regards