95 grand am over heating

I have a 95' pontiac grand am with 3.1 auto , and for a while iv notice that its temp easly go's up but not to mutch and only in trafic, but yesterday it when't right up. it seem that my fan isn't working properly, sometime it starts but some time dosent,and when it starts temp goes right down, since i was stuck in trafic it took a while before i could pull over so coolant overflowd .so the light came on "low coolant" i filled her up but the light is still on .what could be my problem with the fan and/or the coolant

First thing is check the coolant sensor, then jump the fan for intermittent power interruption.

As for the coolant sensor, tap on the side of the tank near the front with a small wrench or screwdriver handle, its the float sticking

thanks but i chek' t is and the problem wasnt my fan at all it was my thermostat that was malfunctionning thats what was causing the over heating so iv change it and works a1 now thanks anyways