The coolant level being low could be a leak in the radiator or any of the hoses. Have you looked around the engine/radiator for pink crust left behind when coolant dries?
The bogging could be an incorrect mixture of air/fuel caused by any one of a number of things. Off the top of my head it could be a dying fuel pump, vacuum leak, A/F sensor, dirty MAF, plugged engine air filter, spark plugs, fuel injectors etc.
I would start by trying to figure out where the coolant in the radiator is going. Take off the skid plates and spend some time looking all around the engine bay to see if you can find a leak. Also check your oil and see if it looks brown instead of black which would mean the coolant is getting into the oil.
