Actually right now is the best time to get one for two reasons. You’ve had sex, and you’re past the age that you should be getting them. That’s not to say you should have been getting them already, but at 18 you should probably get one just to make sure you’re healthy. Think of it as a regular physical, you shouldn’t wait until you have a problem, or think you may be at risk, you should get one anyway. 18 is a great age to go see your doctor and get a PAP test.
That being said I don’t think you need to rush to a doctor, there is certainly nothing to worry about. It’s just a good time to get one done. Just like 40 is a good age for men to have a prostate exam.