Insect Bites or Allergic Contact Dermatitis: The description of itchy red bumps that swell and then resolve on their own, especially with the effectiveness of afterbite (an anti-itch medication often used for insect bites), suggests a reaction to an allergen or irritant, such as insect bites or contact dermatitis. The random distribution and the fact that they appear, peak, and then resolve also supports this diagnosis.

Urticaria (Hives): The itchy, swollen nature of the bumps could suggest urticaria, especially if the patient has been experiencing stress, has an underlying infection, or has an allergic reaction to a food or drug.
Eczema (Atopic Dermatitis): Although less likely given the description of the bumps appearing at random parts of the body and resolving quickly, eczema can cause itchy, red patches that can appear anywhere on the body.
Folliculitis: An inflammation of the hair follicles, which can be caused by bacterial or fungal infections, and can present with itchy, red bumps, especially in areas like the groin and back.

Cellulitis: A bacterial skin infection that can cause redness, swelling, and warmth of the skin. It's less likely given the self-resolving nature of the bumps, but if not treated, can lead to serious complications.
Meningococcemia: A severe infection caused by Neisseria meningitidis, which can present with a rash. Although the rash in meningococcemia is typically more widespread and accompanied by severe systemic symptoms, any rash that could potentially be a sign of a life-threatening condition should be considered.
Lymphoma or Leukemia: Certain types of lymphoma or leukemia can cause skin lesions, although these would typically be accompanied by other systemic symptoms such as weight loss, fever, or lymphadenopathy.

Erythema Multiforme: A skin condition characterized by target lesions, which can be itchy and appear in response to infections or medications. It's less common and typically has a distinctive "target" appearance.
Sweet Syndrome (Acute Febrile Neutrophilic Dermatosis): Characterized by fever, leukocytosis, and tender, erythematous skin lesions, which can appear similar to the described bumps but are usually accompanied by systemic symptoms.
Dermatitis Herpetiformis: A chronic skin condition characterized by blisters filled with a watery fluid, which can be itchy and appear on the elbows, knees, and buttocks. It's associated with celiac disease and would be an unusual presentation for the described symptoms.