Decayed tooth and i have bad breath now is this common ?

Yes : Decay is caused by bacteria digesting sugar and producing an acid that destroys the surface of the tooth. Filling the tooth will help, but you must brush at least 2 times a day for 2 minutes and floss at least once a day to keep your teeth free of sugars the bacteria can digest. Visit the dentist twice a year to check for decay and signs of gingivitis or bone disease (periodontitis).

Bacteria Cause Both!: Here is a simple explanation of the common oral problems. Tooth decay is caused by plaque which is the sticky stuff that forms on teeth. It contains billions of bacteria which eat the food you eat and produce acids as their waste which desolves the teeth. The same bacteria irritate the gums so they bleed and the rotting plaque and blood is what causes bad breath.