When mine (chicks) were smelling raunchy I asked in here a couple times about runny poo and stink and too many people assured me this was normal until the day I finally got bloody diarhea! I would get that SelMet stuff and treat them ASAP. If they are not old enough to produce eggs as it is, there is nothing to worry about. If they are producing eggs, you just can not eat the eggs for 2 weeks.
EDIT: I was also told about the apple cidar vinegar and all it did was prolong the disease until I mixed the chicks with the rest of my flock and had to treat EVERYBODY! I say GET THE MEDS! Don't wait.
EDIT 2: If your gut is telling you that something is not right, Listen to yourself. I kept thinking in my head something was wrong and kept getting talked out of treating. Don't make the same mistake.