If you are suffering from a sewage smell, try the following:
Check that all drainage taps (siphons, u bends) are filled up with water. Smells can occur when the pipes dry up and the smell of the sewer can come into the house. In this case, turn on the tap and let the water flow so that the stench trap fills with water.
If your drain in the shower is blocked causing the water to not flow down it, check the drain trap for hair, this is often the cause. Remove the excess hair with a hook if necessary.