What could be causing a certain pain in my leg?

My left leg at the bend (in front) it aches, sort of feels like a sore muscle. Strangely, it pops occasionally, and hurts when it does it. Been going on about 3 weeks now. Can't think or anything I've done, or why it would be feeling this way. Have to take small steps, it's making both my hips hurt to walk funny from it. Ughhh