You didn't say if you were a male or a female. Females tend to get UTI's more often because they have shorter urethra and bacteria have less way to travel to reach the bladder where it settles.
A female can easily get a UTI from wiping the wrong way from the anus to the vagina.
STD's like chlamydia and gonorrhea can cause burning in urethra when urinating. ALso herpes, but most of the time, herpes shows visible blister-like bumps too, so you would know if it were herpes.
Like Heidi has already mentioned it doesn’t have to be an STD if you are experiencing burning sensation while you are urinating. Of course you could presume that it is STD because you had unprotected sexual intercourse so you are afraid of it but it is most likely that you are suffering from urinary tract infection. This is very common condition and it occurs especially in women but men are not exception as well.
I am aware that you don’t want to hear this but you will need to see your doctor. First of all, even if you are right and it is STD you need to get diagnosed and treated. Also, if it is UTI you will need treatment.