Sounds like your water heater wasn't drained and you have some funky stuff in there. I would fill my fresh water tank with a bleach solution and run it through ALL your pipes and fill up the water heater. Leave it in for 24 hours to disinfect and kill any stinky microbes.
Happened to me one year, the wife was very sick during her pregnancy and we abruptly stopped camping early in the season. I neglected to drain the water heater and the water sat all summer long. That fall we had the rotten egg stench. Bleach took care of it.