May have torn my meniscus. What should I do?

See your Physician. If you think you have torn your meniscus your should be examined. Your primary care may feel comfortable making that diagnosis by exam or may order an mri. If you do have a meniscal tear at your age you would be best treated with an arthroscopic surgery done by an orthopedic surgeon. To avoid further injury avoid twisting and squatting, and use ice to help with the pain and swelling.
Evaluation by ortho. An orthopaedic surgeon usually treats injured menisci. You can have your primary care physician perform a routine knee exam to ascertain whether the meniscus is likely torn. Direct palpation over an injured meniscus at the joint line with the knee bent over the side of the exam table will provide convincing reproduction of pain and essentially confirm the diagnosis.