Can a doctor tell if your pregnant by a urine test?

okay im pretty sure i have a UTI (urinary tract infection) and i need to go to the doctor to get medication for it, but i am also behind a couple days on my period and its really starting to worry me. im also 17 and my parents can NOT find out about this..i might be worrying about nothing. but if i go to the doctor and get a urine test done, and i am pregnant, will they know?? i dont want to hear "you need to tell your mom about the missed period" because that isnt gonna happen! hah thank you guys, your help is MUCH needed!