Prostatitis: This condition, which is an inflammation of the prostate gland, can cause changes in semen color, including yellowing. Given the timeframe and symptom, prostatitis is a plausible explanation, especially if the individual has experienced other symptoms like pain or discomfort in the pelvic area.

Urethritis: Inflammation of the urethra can lead to changes in urine and semen, including discoloration. This could be due to an infection, which might not necessarily be sexually transmitted, given the timeframe since the last sexual encounter.
Epididymitis: This is an inflammation of the epididymis, a tube at the back of the testicle that stores and carries sperm. It can cause changes in semen appearance and is often associated with infections.
Semen Infection: A bacterial infection in the semen can cause it to appear yellow or cloudy. This could be related to poor hygiene, an infection, or another underlying condition.

Testicular Cancer: Although rare, testicular cancer can cause changes in semen, including color changes. It's crucial to rule out this possibility, especially if other symptoms like testicular swelling or pain are present.
Gonorrhea or Chlamydia: Despite the timeframe since the last sexual encounter, it's essential to consider sexually transmitted infections (STIs), as some can have a prolonged incubation period or remain asymptomatic for a while.

Sjögren's Syndrome: This autoimmune disorder can affect glands that produce fluids, including semen, potentially altering its appearance.
Amyloidosis: A condition characterized by the deposition of amyloid (a particular type of protein) in various tissues of the body, which can rarely affect the reproductive system and potentially alter semen characteristics.
Genetic Conditions: Certain genetic conditions can affect semen quality and appearance, though these would be extremely rare and likely accompanied by other symptoms or a known family history.