Q: Weird coolant leaks.

So, I recently bought a truck that had a head gasket replaced on it. It drove fine for about 2 weeks, and I did an oil change as the oil in it had sat for around a year and was old anyway. When I cranked the truck back up, it ran fine for 2 or 3 minutes as I was letting the oil run through to look for leaks, then coolant started dumping out around the hose that connects to the thermostat housing. I tightened the seal, and it fixed that leak... so I cranked it again, and once again after it ran for a couple minutes it started dumping coolant everywhere... worse than before this time. Looks as if its coming from the lower radiator hose. I cracked open the radiator cap to see the level of the coolant after it cooled down, and there was a loud hiss and coolant poured out as if the radiator was still hot. Smells like exhaust and there is mud like stuff around the cap, but the coolant itself and the oil are both clean... I can't figure this one out and I need my car running again!

My car has 156000 miles.
My car has an automatic transmission.