How do i know if i have a slab leak?

So my water meter runs when all the water is off in the house and the water in one of are bath tubs stinks when you frist turn it on and the water presure in the kicthen on the cold side is very little almost no cold water at all. I have no pipes in the attic and no warm spots on the floor i cant hear any running water and i checked the yard for wet spots and found none.My house is six years old could it be something else. I do have a sprinkler system it was leaking but i turn it off at the main also the only cut off for the house is at the street.