Unfortunately, there is no over-the-counter pain medication that can be used for cats. All OTC drugs available will be harmful to cats.
If he has an infected tooth, he will need to have it extracted at the veterinarian in order to correct the situation. Repeated use of antibiotics (intermittently), will not correct the problem.
If finances are of concern in this case, there are many organizations that exist to help with this. I am listing some of them here for you to contact and see how they might assist you.American Animal Hospital Association
" Through the AAHA Helping Pets Fund, veterinary care is possible for sick or injured pets even if they have been abandoned or if their owner is experiencing financial hardship."
Angels 4 Animals
"Our services range from financial aid to complete treatment
to those pets and pet owners in need."
A credit card company for health care, including veterinary care.
"With a comprehensive range of plan options, for treatment or procedure fees from $1 to over $25,000, we offer a plan and a low monthly payment to fit comfortably into almost every budget."
Feline Veterinary Emergency Assistance (FVEAP)
http://www.fveap.org/sys-tmpl/door/ "Seniors, People with disabilities, People who have lost their job, Good Samaritans who rescue a cat or kitten - any of these folks may need financial assistance to save a beloved companion." The Feline Veterinary Emergency Assistance Program is a nonprofit 501 (c)(3) organization that provides financial assistance to cat and kitten guardians who are unable to afford veterinary services to save their companions when life-threatening illness or injury strikes.
God's Creatures Ministry
http://www.all-creatures.org/gcm/help-cf.html "This fund helps pay for veterinarian bills for those who need help."
http://www.help-a-pet.org/home.html "Our efforts focus on serving the elderly, the disabled, and the working poor."
http://www.imom.org/ "We are dedicated to insure that no companion animal has to be euthanized simply because their caretaker is financially challenged."
The Pet Fund
http://thepetfund.com/ "The Pet Fund is a registered 501(c)3 nonprofit association that provides financial assistance to owners of domestic animals who need urgent veterinary care."
If you have further questions regarding this matter, please just let me know as I would be happy to address them for you.
Thank you for your help.