Coolant doesnt evaporate that fast. Most likely its time to replace some parts.
As for the oil, my car had that problem too, oil just disappeared. Someone suggested it was being burned up due to poor oil control rings on the pistons. I ran seafoam thru it several times, Crankcase and fueltank, and it hasn't re-occured. Put in about about 1/2 a can in with the oil about 500 miles before an oilchange, empty the rest of the can in with the gas.
98 SSEi 111,222 miles.
Intense PCM, LS6 Valve springs, PEMS, FWI. Hawk Street Pads.