why does my 2005 cheverlot matiz keep overheating?

about 1 year ago i was driving around in my matiz and the heating shot up and began to smoke. I managed to get it back home only to find the water level had dramatically dropped and was smoke everywhere. I left it to cool down and filled it back up with coolant. Ever since i can only drive it about 8ish miles without the heat flying up and i have to put the heating on full to cool it back down. Ive had it checked once and nothing could be found, it definatly is not the head gasket and 1 suggestion was that the thermostat could be broke? Any ideas?