It sounds like your cat is clearly in distress and I would suggest a visit to the vet…sometimes cats get so ill that they need an intervention at the vet. Because they are prey animals, they hide their illnesses and so when they get as ill as you are describing, it’s very serious. In the interim, you may want to try some chlorophyll. White gums are a sign of something seriously wrong.
As far as fleas….I use diatamacous earth in the area outside where my pets go and you can put it on your dogs, dusting it (keeping away from the face so they don’t inhale it) and leaving it on for a day. You also need to treat your house by vacuuming daily, washing their bedding every couple of days. Although I am not a proponent of chemicals, sometimes it gets overwhelming and drastic measures have to take place and if you have fleas in the winter, unless you are in a cold climate, you may need to remove all of your animals and yourself and have a professional come in and get them under control…then completely air your house out before you return.
Good luck with your kitty….I hope he pulls through ok.