I've been diagnosed with runner's dystonia by a neurologist who specializes in movement disorders, although there's no definitive test for runner's dystonia. My symptoms sound very much like yours. My main problem is that my left leg doesn't lift high enough and the ball of my left foot (or sometimes the toe) scuffs the ground as the leg is coming forward. For me, this all developed over the course of 4-5 weeks last summer. A year ago I could barely walk. Now I can walk with only occasional minor scuffing, but it gets much worse running, to the point where I'm afraid to try to run because I trip and fall too often.
About six years earlier I had a much milder form of the same problem, which didn't prevent me from running but was very annoying. After about six months it disappeared suddenly one day. But now it has come back much, much worse.
I'd suggest you see a neurologist who specializes in movement disorders.