It's important to take care of your physical health... and that means going to the doctor EVEN IF you're not sick or in pain. Regular, thorough check ups are critical to maintaining your health and prolonging your life. We've come a long way in medicine and many diseases and illnesses can be treated or prevented by medical intervention. The key is early detection and early intervention. Ignorance is not bliss... At least not in this matter.
And while we're on the subject, I'm going to add that you should always tell the TRUTH and all of the details. There is nothing you should ever keep from your physician. Ever. No excuses. If you're embarrassed, get over it. If you're afraid you'll get in trouble, get over it. (As a matter of fact, the moment you turn 18, your doctor CANNOT talk to your parents about your medical condition without your expressed permission. If you're under age, you can always ask your parents for some privacy with the doctor. They'll understand, trust me. They'd rather you do that than keep something from him or lie.