Re: Infant (3 months) Failure to Thrive. Chance of CF
DS was diagnosed shortly after he was born due to a bowel obstruction caused by meconium illeus. He has to take digestive enzymes due to pancreatic insufficiency -- without them he was very loose and frequent stools. When he was a baby I'd sometimes have to change him three times during one diaper change because he'd just keep pooping. Is your child's poop different from your other children's when they were babies? Is it more frequent, different color, smell....?
DS also had very thick nasal mucus. We'd have to use saline drops and the dreaded bulb syringe to try to get them out, so he could eat/breathe. His nose NEVER runs because the mucus is so thick.
He did wheeze during the winter months, but by then we were prescribed chest physiotherapy (CPT) and nebs to get rid of it. CF doctors wanted there to be no cough.
Does your baby taste salty? When you kiss her do your lips taste salty?
IMO, she does appear to have some symptoms. Does your state have newborn screening. There's obviously something going on with her, so ask your doctor to do some preliminary testing -- to rule out cf, to get her symptoms treated -- whatever may be causing it. Please note that a lot of family practice doctors aren't all that familiar wcf, so you may need to be a bit pushy; however, a parent knows in their gut that something isn't quite right with their child in terms of health issues.