While those infections listed by GuitarRox are possible, they aren't at all likely just from licking a penis for a few seconds. Chances of you getting anything from that are probably zero.
Licking a penis falls under the category of oral sex which does have STD risks associated with it. Using a condom or barrier helps eliminate that risk. Risks: chlamydia, gonorrhea, hpv, herpes or syphilis. https://www.cdc.gov/std/healthcomm/stdfact-stdriskandoralsex.htm Routine testing isn't a bad idea if you have never been tested but typically, these things result in a tell tale symptom that you would want to investigate if you have that.