If you do have a genital infection, it's a very bad idea to leave it untreated.
But most infections can be treated (and cured) very easily - you just need to see a doctor.
As Gumdrop said, it's perfectly normal to get a "discharge" of pre-ejaculate when you're sexually aroused (or, for example, to ejaculate during sleep - a "wet dream"). You only need to worry if you're getting a discharge from your penis for no reason, or if it's an odd colour. If either of those is true, then you should see a doctor.