A lump inside the lower eyelid with redness below the eye

There are several causes for a lump and redness under the dog’s lower eyelid; common ones include heat, third-eyelid hyperplasia, trauma infection, foreign objects, and entropion conjunctivitis. From your brief description it is likely eye inflammation, but third-eyelid hyperplasia cannot be ruled out; such inflammation or hyperplasia causes redness, tearing, eye discharge, and scratching. First put a collar on the dog to prevent scratching, then apply neomycin sulfate eye drops 4 to 6 times daily. If there is no improvement in three days, go to a professional ophthalmology exam for diagnosis and treatment.