Left mouse key isn't working right

It works, but not like it used to. It takes me pressing the left key at least three times before an action is performed. This naturally makes doing anything excruciating because I have to spam click left. And it works just fine if my character is standing still but takes three or more clicks to work when moving or just after I've moved.

I don't know what's wrong. It hasn't been this way before and I genuinely need help fixing this.