Awwww, what a great person you are to rescue this kitty.
So is Similac the human baby formula? If so, it does not have all the essential amino acids that a cat requires such as taurine, which can cause heart failure if a cat does not get it.
Your kitten is loosing a lot of fluid and should really only be on a canned diet. Wellness kitten canned
is the best you can buy. It is sold internationally at quality pet food stores. You can add some KMR to it to add some fluid.
If the discharge is green and any variation of green you need to see a vet. This indicates a bacterial infection.
Please only give meds to a cat that have been prescribed by a vet. Some very minor human meds can kill a cat.
L lysine may help in keeping the herpes virus (kitty colds) at bay, along with a very good, high quality diet.
Here is a great website on cat food: