My waste keeps backing up into the shower. I have snaked and had the city flush the main. The wste will not follow the snake to the main sewer, it just sits at the cleanout and then backup in the shower.

I've lived in this 4 year old house since it was built. This summer, I noticed periodically a horrible sewer smell coming from the floor drain in the basement, which was remedied by pouring water down it. The frequency that this procedure has to happen is intensifying - to now, where I have to pour 2 gallons of water every two days to keep the smell from returning. I live near the bottom of a hill, have not asked any neighbors if they're experiencing similar problems - there is a lot of construction going on in our area. Is there any method to solve this permanently or at least less often and could it be associated with the large addition going in behind me - such as too many houses on the sewer line, so it's backing up, or drying out, or what?? I've had a plumber look at it, and he says for some reason that water in the trap is fluctuating up and down quite a bit but he doesn't understand why.