ugg fml
cant figure out whats wrong with my truck

originally i thought my thermostat was going out which wouldnt be bad to replace, but now im thinking i have a coolant leak somewhere cuz i just went and checked my resevoir and it was almost completely empty, so i refilled it, drove for like 5 miles came back checked it again and it was low, so i refilled and did the same thing came back and low again!!
but its not leaving puddles or anything so i dunno wtf to do lol..