Do I need to apply more flea oil to my cat?

No, it does not wash off after about 48 hours or so. You cannot reapply it more frequently than once a month. While I understand your financial situation, in the long run Frontline or Advantage would have been cheaper. Call your local shelters - many of them will sell you one vial of either of these, which only costs about $15. I am sure you've spent that much already on products that do not work. If you continue to apply flea treatments on him, you run the risk of poisoning him - which is going to cost significant $$$$ at the emergency vet.