Hard,red, tender lump is suggestive for an early stage of an abscess (collection of pus underneath a portion of skin, due to infection with bacteria that had entered the skin through any cracks or injury to the skin)
The most important treatment for small, and, hard abscess is heat application, with hot soaks or hot packs (soak at least 3 or 4 times a day, 10-15 minutes each time).
Once the abscess or boil becomes soft or "forms a head", will drain on it own with soaking.
If this lump becomes bigger, more painful with increased redness of affected area, or, accompanied with fever, you should seek medical attention.
Have you been on meds recently?
Do you suffer from a chronic medical condition, like diabetes?