Depo-Provera - does the shot change the pH balance, because my vagina isn't producing its natural..

The Shot definitely made sex dry & painful for me. At times I'd produce a lot of thick, cervical mucus, then I'd be very dry & sex would be painful.
The spotting got less as I had more shots. Usually 2 or 3 shots then the irregular bleeding is very little to none. Everyone is different, though.
Sometimes I'd spot a little before my shots were due. Getting my shot as early in the window they usually give, would help that.