It sounds like the best thing for you to do in this situation is to see your primary care physician
right away for a more thorough history and physical exam. In this situation your overall health history, age, and family history might be important in taking care of your issue. It is certainly possible that this is purely a musculoskeletal problem, such as a torn muscle, tendon, or ligament. However, you may have developed a more significant injury
that would require orthopedic intervention. Similarly, it is also possible for minor trauma during sports activity such as what you describe to cause the rupture of a cyst behind the knee. This is called a Baker's cyst and might also explain some of the pain you are experiencing. In order to make sure that your health is okay and that you don't need further imaging or evaluation with an orthopedist, you will need a thorough exam as well as a review of your medical history. Your primary care physician should be able to do that, and if it does look like you may simply have a muscle strain
, a referral to physical therapy might help you recover faster. In addition, pain medication or anti-inflammatory might also be helpful.