6.5 Month Old with Rash

It could also be eczema. Have you tried moisturizing? Daily washing could actually exacerbate the situation. My second was (and is, at 3.5) very rash-prone. Oodles of a good lotion usually does the trick. There are also some viruses that come with a rash, which I am sure you know if you have 2 others, so keep an eye out for fever or other symptoms.
And detergent, fabric softeners, or dryer sheets can cause skin irritation, possible culprits. Because if you are on baby #3, I know for darn sure you aren't using expensive "baby detergent." Dye-free, fragrance-free anything is usually fine.

Not sure about the whitish...but the red bumps could be from drooling or exema. My kids all got a rash on their chin/neck from drooling and my youngest has exema so it's more of patchy bumps. I would call the dr but most likely they will tell you to use an anti-fungal, hydrocortosine or bacatracin.

could it be food allergies? I know that my daughter had skin issues until I got her off cows milk.

It's probably just a virus. Babies get tons of them, nothing to worry about unless she seems fussy. Otherwise, it will probably just go away in a day or do.

Does she drool a lot? Could be drool keeping things damp, leading to a little thrush. Easy to check - try some lotrimin cream on 1 small spot, and see if it clears up within a day.

whitish red?
my girl had baby acne that would come and go.

Since it isn't getting better, I would probably call the nurse hotline or make an appt to have them look her over. It's better to get their opinion then to get guesses from us.