Knee weakness, pain, after excersize since dec., still now, dumb and bruised. pops sometimes. what's wrong?

See a Dr.: If you have had this issue since december, don't wait the problem out and hope it improved on it's own. Get evaluated before you create a permanent injury (if not already.).

Stretch strengthen: Popping might just be from the underside of knee cap. Joints need to be reinforced by the muscles around them - so strengthening your quadriceps and hamstrings are important. Additionally the iliotibial band can refer with knee issues - so I am a big proponent of foam rolling.. Stretch, strengthen and foam roll - and of course make sure you have the right shoes!