I'm sorry to hear about the pain behind your left knee. Since the medications you took—Gabapin NT (which typically contains gabapentin and a pain reliever) and Meganeuron OD Plus (a vitamin supplement for nerve health)—have not relieved your pain, it’s important to consider other causes and next steps.

Here are some suggestions:

• Rest and avoid activities that worsen the pain.
• Apply ice packs to the area for 15-20 minutes several times a day to reduce inflammation.
• Try gentle stretching if it does not increase pain.
• Monitor for any additional symptoms such as swelling, redness, warmth, fever, or difficulty walking, which may indicate infection or a more serious issue.

Since the pain has persisted for four days without improvement, it is important to see an orthopedic specialist or a sports medicine doctor. They can perform a physical examination and may recommend imaging tests like an ultrasound or MRI to identify the cause, such as a ligament injury, tendonitis, bursitis, or other knee problems.

If you experience sudden severe pain, swelling, inability to move the knee, or signs of infection, seek emergency care immediately.

Please consult an orthopedic doctor promptly to get an accurate diagnosis and appropriate treatment.To narrow down potential causes, we will need some more information.I understand you're experiencing pain behind your left knee and the medication you took didn't help. To better assist you, could you please provide your age and gender?