Hi...
Is there a check valve in an air bladder water holding tank?
My pressure fluctuates, the pump is working but pressure slowly decreases and empties if I use my washer.

There is not a check valve in a bladder tank. However, there could still be a blockage somewhere in the pipe rusticating the flow. I have take the traditional style of tanks loose to try and find blockages, and found big chunks of calcium, floats from old mechanical floats, a pocket knife one time, etc. One other thing is that you may have a gate valve not opening all of the way. In the trade we call it dropping the gate, since the gate falls off the stem. That gives you a couple of things to check.
Good Luck,
Al