Cyst or Lipoma: A bump that is not painful to touch, not red, and has no drainage, present for a short duration, could likely be a benign growth such as a cyst or lipoma. These are common, usually harmless, and fit the description provided.

Insect Bite or Sting: Although the bump is not painful or red, some insect bites or stings can present with a bump without significant inflammation, especially in the initial stages.
Folliculitis: An inflammation of the hair follicles, which could present as a bump. However, it's less likely given the absence of pain, redness, and drainage.
Benign Tumor: Other types of benign tumors could also present as a bump, though they are less common.

Deep Vein Thrombosis (DVT): Although DVT typically presents with pain, swelling, and warmth of the leg, in some cases, it might not have all these symptoms, especially in the early stages. It's crucial to consider DVT due to its potential for serious complications like pulmonary embolism.
Cellulitis: An infection of the skin and subcutaneous tissues, which can sometimes present without the typical signs of infection like redness and warmth, especially in diabetic or immunocompromised patients.
Abscess: A collection of pus that has built up within the tissue of the body, which might not always drain or show significant signs of infection initially.

Kaposi's Sarcoma: A type of cancer that can cause lesions on the skin, though it's more common in immunocompromised individuals and would be unusual without other symptoms.
Dermatofibroma: A rare, benign growth that can appear as a bump, often resulting from minor injury, insect bite, or trauma.
Panniculitis: Inflammation of the subcutaneous fat, which can cause bumps or nodules under the skin, but it's less common and might have accompanying symptoms like pain or systemic illness.