This could also happen if you dont clean your sink regularly.
Thanks toClean My Spaceon YouTune for this wonderful tutorial!
You also need to double-check to empty the sink traps every day.

Image Credit: Clean My Space via YouTube
After washing the sink, double-check to wipe it dry with a rag or cloth.
You also have to check and clean your p-trap or j-trap regularly to avoid it from smelling.
Pour the boiled vinegar directly into the drain.

*All these images are credited toClean My Spacevia YouTube.
How To Clean A Smelly Sink
