As others have stated, you need to bring your kitty in to see your vet.
Flea collars aren't very effective (IMO) and I would never advise using over the counter flea meds/collars as they can be dangerous.
Two products that I generally like to use are Revolution and Advantage Multi which can only be purchased through a vet and after an exam. I don't know if they are available where you live but they are excellent products used to rid animals of fleas among other things (heartworm, internal parasites etc.)
Again, seeing your vet will give you the opportunity to purchase the best product suited for your cat and will also allow him/her to conclude if they're any other problems (caused by the fleas or otherwise). Good luck!