My mouth keeps watering, but i assume it's from my palate expander. could it be from something else?

Probably: If the expander is relatively new, it's nothing to worry about. If you've had new medications prescribed or medical changes, i'd suggest checking with the prescribing physician. In all likelihood, it's the expander. No worries.

Palatal expander: You are probably correct. If your palatal expander has been placed recently it is stimulating your salavary glands.

Probably, if new: Any new dental appliance will take some getting used to. Increased salivation is common for the first few days, and should then return to normal.