Overheating, Thermostat?

Car overheated on way home, I pulled over let it cool for 30 minutes. It only made it 5 miles up the freeway and overheated again. I parked the car for the night 30 degrees outside. Went back the next night to try and finish the 16 miles home and it overheated again. I had to drive 1-1.5 miles once the light came on to safely exit. pulled over and opened hood and was like a steam factory. The only place i can tell is the coolant is exiting the pressure cap. I popped the cap off and coolant really pressurized and boiling. the drivers side house leading to thermostat housing was boiling hot, passenger side cool to the touch. the head was steaming this time also, however did not see any coolant in oil on dipstick? also when car started to over heat heard a clicking and the heater quit blowing hot air? Is this a thermostat or Water pump issue? or both? I hope that i didn't crack the block or lose the head gasket...bolts on water pump are not loose either. towed the car home, it started and ran smooth when backing it out of trailer? ideas? answers?

thanks