ok, so I bought this trek 7100 about 10 years ago....

I rode it about 300 miles because the rear wheel always broke spoke every other ride it seemed (probably not that bad but it was bad)... so the bike shop basically said that because of the type of bike (hybrid rather than road) that I being a heavier kind of guy was putting more stress on the rear wheel and that I need a more substantial wheel.

I was annoyed with that, so I bought a bikes direct type of bike soon after (lightning sport) which was a retro type of bike, stem shifters, etc... I rode that bike for over 2000 miles (I was into biking, then not so much, now I am into it again) and never broke a spoke on that bike (it has drop down handlebars by the way...) and I kept the trek in the basement, not sure what to do with it...

so I decide I want to start bike commuting and decided to take the LBS advice about a more substantial wheel, so they ordered me a 36 spoke tandem wheel for the rear. I got it on my bike about a year ago and was starting to like the bike again. the road bike wheel is a 32 spoke wheel, by the way...

now recently, I broke a spoke and took it back to the shop, they fixed it and a week later, I have another spoke broken. Now, I am having flashbacks to the original wheel problems...

whats the problem with the spokes? are they really more stressed on the hybrid than the road bike?
what would you suggest to finally fix the problem?