This article tells you how to use vinegar and baking soda!
If you have a garbage disposal for food, you might grind some citrus peel in it on a regular basis. If you have no disposal, try spraying it several shots of Simple Green that deodorizes and disinfects. If those two do not work, you may have the sewer gas coming up and need to put in an S curve to trap liquids to prevent sewer gas backup. Hope one of these ideas helps, Lucy.
Use this to clean the drain. Remove as much as possible with a snake or drain cleaning tool. Pour ½ cup baking soda then ½ cup white vinegar in the drain and cover, letting sit for 20 minutes. Boil water, remove cover, and pour water down the drain. You may have to repeat the process.