Sitting cross legged that on floor strains your knees, usually such symptoms are more common in elder age group after 50 years. your getting such symptoms early so avoid sitting cross legged Some people tighten muscles & ligaments especially Illotibialband around knee these symptoms comes,if so meet orthopedic surgeon ,May require physiotherapy. the blocking symptoms are nothing but numbness due to nerve compression due that postural, that's not a worrying symptoms

though knee pain at your age is uncommon , numbness due to decreased circulation is a frequently encountered among middle aged population, please avoid sitting cross legged for a few weeks, go a walk regularly, if possible TRY cycling, local hot fomentation is also helpful. in case symptoms persist even after a month following the above modifications, please consult a doctor