My knee pops when i extend to straighten my leg its not painful but fell over and hit knee hard 2 years ago and it just doesn't look the same as my other knee seems fluidy any ideas?

You might have torn a ligament at that time. I tore 3 ligaments (ACL, PCL, MCL), and got fluid in it. You can have it drained at your family physican. My friend had hers drained. I have heard that its painful, but I never had mine drained. Just something to think about.