1990 Ford Bronco Coolant emptying

My Bronco recently began to overheat and the vent quit blowing warm air and began blowing cold air. I checked the coolant level, and it was ridicously low. I had checked it a few weeks back, and the level seemed fine.

I filled the radiator with coolant and the next time I drove it, the same thing happened all over again.

I'm not seeing any visible leaks anywhere, but that coolant has to be going somewhere. Any help?