I agree with both above. A bit of light yellowish discharge can be normal for a male dog but if you never noticed it before and if you see blood at least phone your Vet. My own boy has just finished a ten day course of antibiotic for a UTI. Something that helped me was to check the snow every time he pee'd, and I saw blood in the snow. Once it was solid, bright red, very scary. He's all better right now.
One thing your Vet will probably want is a urine sample. Take this first thing in the morning, his first pee after being in all night. You might find a helper necessary. One of you walk him on leash, the other slips a clean container (soup ladle works really well) into the stream of urine to collect it. Place in clean glass jar with lid and refrigerate if you can't get to the Vet till later in the day. Bleach soup ladle. Or buy a new one.
