Found an over flow in our bathroom. When we checked the shower. There,me were small particles on the floor of the shower. Now there is sewage smell coming from the shower drain.

The smell might be sewage or just stagnated build up of a mix of things . try to use a plunger to make sure your shower drain is not blocked in any way , to use a plunger correctly you will need to block the drain hole and fill the shower with hot water and remove what you have covered the drain with and start plunging while the water is running down the drain , this gives maximum effect while using your plunger , some material may want to expel out the top of the drain while other material will be forced down and along the waste pipe after you have done this pour a large cup or two full of liquid bleach down the shower drain and see if this clears the problem ,because most sewer systems are independent from the waste water of sinks, showers and washing machines. Also when you flush the toilet try adding a bucket of water at the same time as you press the flusher , this will force more water than usual down your toilet helping to keep the pipes fully open , but if you notice that when you flush and add the bucket into the bowl at the same time that the water does not escape freely and seems to back up , this can be a sign that there may be blockages in the sewer pipes and you might try doing this extra water flush a few ,more time hoping you will clear your pipes adding some Landry washing powder to the bucket can have a effect on moving anything along and hot water is beneficial as well . But I think you will find that the shower drain is what is causing the odour pouring a mix of vinegar and baking soda down the drain as a regular maintenance job keeps them odour free and unblocked .