My 12-year old son has been sick off-and-on for a month. every time we think we've kicked it, it'll come back a week later. what should i do?

Seek help: Hard to diagnose on this forum. Don't know enough about your son. He may have a compromised immune system or some other systemic problem that is not letting him fight off infections. Please have him examined by a physician asap.

Being sick: So sorry to hear about your child's health troubles. At this juncture, he deserves further testing. I usually start out with good history & physical exam. If i need to proceed with further testing, i get general health panels such as cbc, chemistry, thyroid function to begin with.

Seek help: It's best that you seek a pediatrician for further evaluation.