Losing coolant, again.

Pretty much the title. I did the notorious heater hose lines and all coolant lines about 3 months ago after I noticed it was leaking. Drained and filled the coolant and burped it. When I was done the coolant was just over the max line. Today I went to check on the oil and everything else after about 3k miles and I noticed the coolant was just under the min line. I checked the hoses, water pump and thermostat and didn’t visually see anything. My question is could there be enough trapped air in the system that after 3k miles it dropped that much? or could I be dealing with a cracked head? Previous owner said that water pump and thermostat was done at some point, but now at 110k I don’t know how long ago it was. Any ideas would be appreciated.