Welcome to the wondrous world of the seductive W-220 S-class.
The Airmatic suspension seems to be both a blessing and a curse and there are both pros and cons associated with it. You are now experiencing one of the cons.
Based on your description, here is what I've learned from researching a similar challenge.
First, there are 3 fuse-boxes for this model Mercedes. Find the diagram of your fuse-boxes and their associated components in the toolkit above the spare tire in your trunk. Look closely, because the diagram is kind of hidden. If it's there, you'll find it wedged between a wrench.
You may want to check three relays first. One, the "Air Compressor/Airmatic Relay" (K40/7KO) and the "Pump Circuit Fuse" (K40/7f32) both are in the right side box in the engine compartment, in front of the passenger seat.
The third relay is on the driver side, left side fuse-box, the "Air Pump Relay" (N10/1kr). If the contacts are intact on your relays, move on to point 2. If the contacts are not intact then perhaps a replacement will solve the problem.
Second, there may be a leak in a hose where the Aiirmatic line meets the strut. Supposedly, these rubber air intake hoses are available through Autozone.
Third, the Airmatic suspension pump may be malfunctioning. Supposedly, the pump is not difficult to replace. It's located under plastic protective covers up inside the fender, behind the front bumper and the passenger side headlight.
Fourth, you may need new struts, but hopefully that's a last resort.
That's what I've got for you, thus far.