Welcome to JA,
It either has some trash stuck in it or it has stripped. I would open it and blow some compressed air into it and see if that will clear it. if not it will have to be replaced.
It sounds like the t knob has broken loose from the spout. If that is the case there should be a nut behind it you can use a wrench on to turn the whole thing out to replace it.
Which one of these does yours look like?
If it is like the black one it is locked from the inside with a couple of plastic ears. It will have to be forcibly removed and the new one will just push in and lock.