Kudos for taking on the challenge of getting exercise and generally looking for a more active lifestyle.

There's no doubt that the rear wheel usually takes more of the load on most bicycles since we generally area positioned so that more of our weight is to the rear on most bicycles. So that's a factor for starters.

Second is that as odd as it sounds spokes are very tough when under tension. When they break it's mostly because they get loose as they pass over the bottom of the rotation and then get jammed between the rim and the hub if or when the tension goes to zero load. Eventually metal fatigue occurs and they break as they go around the top. We actually are hanging from the spokes around the top half of the wheel when riding.

Now on the rear the drive side has more tension on it so the spokes on the drive (cog) side will almost never loose all their tension. But on the non drive side they run with less tension due to the offset or dish of the wheel. And sure enough it's the non drive side with the lower tension that you're breaking the spokes on.

What I'd suggest is that you find a shop that can build a good wheel and request that they rebuild your rear wheel with good quality 14 gauge spokes and run the build up to a higher tension all around than they usually do. This way your non drive side is running closer to or up around what your present drive side setup has for tension. This way your weight won't let the spokes reach a zero tensile load at any point in the rotation. And that's the key.

You can even test this for yourself. Tap the drive side spokes with a plastic handle screwdriver and note the tone. Do the same to the non drive side. Note the higher tone and try to remember it. After your wheel comes back from the rebuild tap the non drive and see if it's around the same sound as your present drive side.

The reason you need to dump your present spokes is that they have already fatigued from the riding you've done on the bike. It's because they are now weakened that they are all of a sudden letting go. You don't want to trust any of them at this point as even if you get the shop to run up the tension there's an excellent chance that the non drive spokes will just keep breaking. Now the drive side spokes may be all right but for the sake of a few dollars it is false economy to trust them. That's why I say replace them all and rebuild your wheel from the ground up.

That WTB rim looks pretty sturdy from what I see but if the shop recomends a more bomb proof option you may want to consider it at least for the time being just as insurance. There's some nice options now thanks to the 29'er trail bike movement. This is off road riding with tires and rims that are the same overall diameters as the 700c wheels but often build extra sturdy.