well I think you should take the day off for the broken fingernails hun!
As for the bike:
If the mechanic says the rear wheel isn't tight enough - then ask him to please show you how to tighten it. Also, does he test ride it when he's done working on it?? Not only does my LBS guy show me what he's doing, but he test rides Every bike he works on before he lets it out of his work area. (and I gotta tell ya....seeing a 6' bear of a guy riding my itty bitty 50 frame with the seat and stem all the way down is hilarious!!) Ask him to take it out for a ride before you have him look at it, and then after he's done. See if that helps any.
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, champagne in one hand, strawberries in the other, body thoroughly used up, totally worn out and screaming: "Yeah Baby! What a Ride!"