You shouldn't need new pads after three two hour rides. What you may need are decent pads. My Sequoia came with crappy pads that made all kinds of noise and didn't stop worth a darn. I replaced them with Kool Stops and problem solved. You may have picked up junk on the side of your rim as well. Try cleaning it with denatured alcohol (you can get it at Home Depot).
You "fixed my rear brake" and now it feels weak sounds like you need to tighten up the brake cable. You can try using the barrel adjuster to tighten it a bit. If that's not enough, undo the cable and pull it tighter before clamping it back down.