@lapsed - I’m in the same boat as you: leg pain with no apparent reason. I’ve had all the tests done as well and they’ve come back clean. I can try to offer a few tips on how to deal with the pain that have worked for me.
One thing that helps a lot is to take hot baths regularly as heat is great for loosening up and relaxing muscles. You can also try stretching – tense your legs for ten seconds and then relax for a moment and repeat that a few times. A friend of mine recommended Pilates which I’m yet to try but could be promising. Hope this helps!