What type of over the counter pain reliever and how much can I give a 13 yr old Chihuahua?

She weighs about 7 pounds and is otherwise in good health. I know she is uncomfortable..She has a heating pad in her "Condo". She likes to lay on that..Or in the sunshine.She moves around fine..up and down few steps but, she is limping a little. Taking her to the Vet is not an option..Sorry to say. I can't afford to go to the doctor even..