1999 Pontiac Montana fumey odor

My low-coolant light blinked on then off. Though I have a shortage because my abs and service engine light stays on. I finally checked the antifreeze and it wasn't any. I filled it and it began to get hot. Now there is thick grayish white smoke coming from the exhaust and it has a fumey odor like coolant and oil. I did have the thermostat changed. Bit it is still doing this.