Hello. Thank you for posting your query at DoctorSpring.com
I have read your question with diligence.
It looks from your details that most probably you may have meniscal tear..This is cushion like structure which give support during movements of knee.
At present you should have MRI of knee to get a clear information about this.Till then you should avoid excessive knee bending or walking up or down on stairs.
Hope this will help you.
Feel free to discuss further,