M.R.
Do not stop antibiotics! Keep giving them exactly as scheduled while you also call the doctors office and tell the advice nurse(or triage nurse or whatever your doctors office calls it) about the smell. Ask if you should bring your son in to the doctor. But please never just stop antibiotics on your own; only stop them when the entire prescription is finished or the doctor tells you to stop. The smell likely isn't being caused by the antibiotics but by the infection itself.