S.T.
hm. well, i do think it's a good idea to keep a close eye on it, as your doctor is doing, but it also sounds as if they're scaring you. the weight fluctuation isn't severe, and many kids do boing about a bit when they start becoming more mobile, and are incorporating table food into their diets.
what did she weigh at birth? has her weight gain up to this point been steady?
good for you for continuing to nurse her. i see no reason to switch her to formula (or whole milk, for that matter. your milk has plenty of fat and is far easier for her to digest.)
it's probably pretty stressful for you with 4 kids, and the concern over the weight fluctuations, and very easy for someone from the outside to say 'just relax.'
but my best guess is that your baby is just fine. do keep an eye on it, and do keep nursing her and offering her the food that she's enjoying. try not to let the worry take on a life of its own.
khairete
S.