Why do I have to keep on changing my fit?
Often, I get on my bike and things feel a little off. I put it down to varying fatigue, stiffness, amount of sleep, mood, stress or a hundred other things. I then try to get get warmed up, then concentrate on good technique and having fun, or, if I really am feeling off, cruising along for a bit then getting a coffee.

It sounds like you have trained yourself to be hypersensitive to feeling 'off', then feel the need to need to mess with the saddle position. Maybe you just are not letting you body actually get used to an reasonably OK position. What you need to do is get the position ballpark right, then just stick with it and let your body get used to and adapt to it. I also wonder if regular stretching would make you feel better on the bike.

I'm not surprised that different fits came up with different positions. Bike fittings are not supposed to find your 'perfect position' - that does not exist. They find a good position for a particular purpose. Different fitters may have had a different idea of what you were trying to achieve. Also, I'm not surprised you were slower after each fitting. Your body was not used to the new position and hence you could produce less poswer.