I appreciate your concern towards your health, but you should not take this lightly and should make an attempt to diagnose the injury.
You should be seeing an orthopedist as early as possible and get imaging study done to see for any injury. Imaging study should be MRI to look for soft tissue pathology.
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 joint line is the result of a collateral ligament or meniscus problem (or both) until proven otherwise.
Your symptom of sudden pain, then hearing a pop and swelling suggests that you have ligament injury. If the patient has a ligament injury, the patient will report a deceleration injury or twisting the knee that led to immediate symptoms of swelling and pain. In fact, 30 to 50% of patients will report actually hearing a “pop” at the time of injury.
Your symptom of locking and catching are characteristic of meniscus injuries.
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?
Keep me informed if you have any queries.