Painful lumps in the area you have described are most likely due to infectious cause. This is because you describe the lump as being very painful to touch. Most of these cases are due to folliculitis
in which a hair follicle gets infected. The lump is restricted to the skin because it does not seem to move under the skin. In deep seated lesions, an overlying redness
might take same time to appear but it eventually does as the infection gets localized. In any case, it is safe to consult a doctor before you can start off any specific medications for the same.