How are you feeling?
When any patient complains of “knee pain,” the initial differential diagnosis in most of the cases includes: Osteoarthritis, Ligament damage, Meniscus damage or Patello-femoral disorder.
Your symptom of pain at the posterior part with swelling suggests that it might be due some collection like Baker's cyst.
Otherwise it appears to be due some ligament or meniscus tear.
Your history of starting of pain while playing basketball and you being not aware of it suggests that it might be due to meniscus injury.
Do you experience any grinding, locking, catching, or giving way of the knee?
Are there any positions that make your knee more or less comfortable?
What is the quality of your pain (sharp, shooting, dull, etc.)?
Have you tried anything to help the pain and, if yes, has that been successful?
Have you ever had surgery on your knee? Do you have any hip or ankle pain (both hip and ankle pain can refer pain to the knee, and vice versa)?
Keep me informed.