I'm 33 (is that relevant) and just had a baby (probably not relevant) and have developed excruciating pain in both knees.
It's so bad I feel like I need a crutch, I find it hard to get up from a seated position or to walk up and down stairs.
It's in the front of the knee and is almost burning. I can move my knees all around and stretch them both fully but it is really painful.
I didn't slip, fall or injure myself in any way and am totally bewildered as to what is causing this.
Can you go to the doctor with a sore knee? 
Any advice?