what could problem be when engine overheats, low coolant light on, temp ind. on

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I have car for several months, ran a little hot(my opinion) not good gas mileage. Began to run rough. Stopped car. When started then began to overheat stopped car found loose connection that plugged into back of radiator on side by fill bag, black sensor type plugged back in refilled fluid. Using lots of fluid but not leaking out anywhere. Temp begins to increase when engine is turned on and low coolant light comes on, when refill coolant temp drop light and indicator go off and then everything happens again fluid is drained into radiator, lights and indicator come on, temp gauge rapidly rises, no fluid appears underneath car or anywhere under or around engine,.