problem with coolant level

i had recently add a galon of coolant to a coolant tank, it was exactly on 0ct 28, today i checked coolant and the level is lower than its supposed to be, can somebody give me an advice what can be wrong, at the time when mechanic add coolant, they also replace a water pump, because it was leaking

0n oct 28 mechanic added a coolant to my car, it was a gallon, but i checked today coolant, today is nov 16 and level is lower than its supposed to be, mechanic also replaced a water pump, because it was leaking, can somebody give me an advice, what is wrong, or what to do

Check your oil. You may have a leaking manifold gasket, which is allowing coolant into the oil. Remove your oil filler cap and if you have a bunch of white gunk inside of the valve cover, that's it. This is a very common problem with the 3.1 V6 because they have aluminum cylinder heads.