Carrots are rich in carotenes, which are substances related to vitamin A. They're found in the orange pigments and are good for you, but, if you eat lots and lots of carrots, you can develop a yellowish or orange cast to your skin. It's mostly noticeable on the soles of your feet and the palms of your hands.
Benadryl is another decongestant safe for use in cats, although it is usually not as effective as chlortrimeton in treating congestion. Benadryl is generally more beneficial with treating snake bites, reactions to vaccinations, itching, and insect bites.
Prozac is a brand name for fluoxetine, which is also marketed for cats under the name Reconcile. Fluoxetine is a selective serotonin reuptake inhibitor, which means it increases levels of serotonin in your cat's central nervous system. It won't work overnight -- it could take as long as month before you'd see a difference in your cat's behavior.