I am sorry to hear you are worried about about Charlie having Discoid Lupus. My name is Rebecca. I am a veterinarian and will do my best to help.
This is usually treated with minocycline or doxycycline, or else tacrolimus ointment. These are all available from your veterinarian, or from a pharmacy or online pharmacy but with a prescription from a veterinarian who has examined Charlie. These are not available over the counter.
You could try topical cortisone ointment, which is available over the counter but usually is not as effective as the prescription medications I mentioned.
Let me know if this helps, and what other questions you have.
How is Charlie? Can I help with anything else?