switching remedies

I was wondering how long you wait in between to change remedies if you believe something isn't working. I mean like if your treating a cold that doesn't seem to be responding. If I were treating myself it's pretty easy, however, when treating children sometimes so many remedies seem to fit. Just wondering how long I should give something until changing. Sometimes, they will develop a new symptom, and then it makes me think I need to give them something different. For instance, my baby with bronchitis cleared up practically overnight from using the belladonna, but my daughter who is 9, started out like the baby, but ended up with a fever, and all stayed in the nose instead of heading to the chest. She is complaining of her lower back hurting too, and a tummy ache. I'm not sure with her activity, if the back thing is related to the illness. I've had pretty good luck treating sniffles and coughs with homeopathics. They seem to work faster than waiting for vit. c and garlic and other herbs to kick in. Please advise, as I have been doing herbs and other natural remedies for years, but fairly new to the homeopathic tablets.