coolant on 2004 Volvo S60

I have to add coolant every couple months but i don't see a leak, is there something i'm missing?

2 answers
I would suggest pressure tesing the cooling system and adding dye. If the pressure drops, there is a leak. You also could be burning coolant, which would indicate a possible cylinder head gasket issue.
Check at the bottom of the radiator, on the sides for signs of coolant. The radiators leak quite often on these and it's a good chance this may be your leak.