About 10 days ago my main line backed up into my kitchen sinks and shower while I was doing a load of laundry. My plumber came and cleared everything but ever since I have smelled a musty, moldy odor only in my bathroom. Is this a sign of mold somewhere? I have cleaned the shower, the floor (no carpet) and the sinks...

Yes that smell usually indicates that there is still moisture. If your shower is not properly sealed the moisture could've gotten under the floor or around the shower, faucets, surrounds, toilets. Check to see if your bathroom is sealed properly, look for anyplace water can go, behind trim, where cabinets and floor meets etc...