1993 Honda Accord

I have a 1993 honda accord 10th anni. I began to hear a slight knocking in the engine which goes away once the car warms up. It started over heating a week or two later. I noticed coolant being blown back into the resevoir tank which makes a loud bubbling sound. When I opened the radiator it was totally rusted. I took out the thermostat to see if that was the problem, but it overheatd juss the same. I then replaced the thermostat and the radiator(using a 50/50 coolant/water). It ran fine for a day or 2 then started the overheating again and I cant recall hearing the cooling fans tripping in either. The knocking sound, seems to be getting louder. Is the cooling system blocked or (i fear) do I have a blown head gasket/cracked head?