My best friend had the same issue on a bike that he got from his dad. It is a 1999 Trek Y3 that has sat for the past 5 years (since his dad got his Trek Liquid) and when he since he started riding it this summer he has broken close to 5 spokes. He has decided to respoke the wheel seeing as it has a pretty good bontrager rim and shimano hub. You are either gonna have to either get a new wheel or respoke your current one.

Also, make sure to check the spokes your LBS is putting into your wheel. The LBS that was replacing the spokes for my friend for some reason was using the wrong sized spokes. He had one spoke that was so long that it went through the second wall of the rim and into the tube and he had another one that was double butted (the rim has regular spokes). Needless to say, he isn't going to that LBS anymore.