Coolant Leak in the cabin?
 

Weeks ago I change almost the whole cooling system (radiator, upper hose, thermostat, thermo switch, housing, expansion tank and cap) and has been working perfectly but today I check the levels, the coolant was low and the driver carpet is wet.

How is that?

Any ideas where can this leak comes? where to seek for the hose leaking or something else...?

Sounds like a leaking heater core.

its also possible the work moved the hoses that go from the block to the heater core that disrupted the o-rings that seal the hoses into the heater core. either way you'd need to open the console sides to inspect. Replacement heater cores are not that expensive so you may want to consider doing the hoses, new o rings and new heater core and be back to like new condition.