I believe my 4 week old infant has a yeast infection in his little neck rolls. Do we need to make an appointment to come in for some medication?

Depends. It is more common for u to see prickly heat there. Until babies neck grows longer & the skin on skin quits trapping sweat, the moisture often produces tiny red dots or raw skin. Lifting the folds, bathing the area & blowing dry with a lo heat hair dryer can help. If the red bumps are rough to touch, it could be yeast & some antifungal cream might be needed. Call the office during regular hours for rx.
Yeast infection. It happens due to humidity. Try to keep the area dry, you can use some of the powder to help you keep the area dry. If there is already a fungal infection, you will need a prescription for nystatin.
Probably. The key to a good treatment is proper diagnosis. The redness in the neck folds could very well be yeast, but it could just be skin irritation too, or a rash relating to something else. Before bringing your little one in, do what you can to keep the area dry, and if it doesn't get better in a day or two, make an appointment to see your doctor.