After installing expansion tank, massive buildup of pressure then a trickle?
Sorry to hear about your "odor" problem. Maybe there is a local public fountain you can take a dip into!!!

However, the problems you describe are fairly common, but may be tricky to isolate. Let's try some basics:
 Relieve the pressure from the bladder completely. Let the well pump fill the tank completely  and bleed any air from the system using the faucets with the pump running. Again, with the tank full of water, close all outlets and charge up the bladder to about 60PSI.  Most systems work fine between 45 to 65 PSI. Anything over 70 is pushing it. The tank needs to be charged when full, not empty.
Monitor the pressure as you draw water. Does the pump kick on constantly when the pressure reaches the low limit, and off at the high limit? This will help tell if the regulator is working properly.

Is there any pulsating water pressure at the faucets? 

When you are sure you have a full tank, no air in the system, is your second floor water flow ample when the tank is reading 60psi?

There are a few "if's" here. Depending on how the pump behaves and the pressure responds, you have to determine if the problem is with the pump and volume of water being delivered to the tank, or if the pressure regulator is properly operating.

If you are still seeing any pulsating water pressure at the taps, then the bladder is water logged again.  If the bladder pressure drops too quickly, then most likely the volume of water from the pump is low. The pressure should remain fairly constant at the tank if all the functions of the pump and regulator are working properly.  Good Luck