First, major props to you for three things:
1. Despite your health problems, you clearly have some significant strength to hoist those bales and bags
2. You've made some corrective actions already, with significant improvements noted
3. You're living a long term responsibility by your own choice, and celebrating it - regardless of which choice is made, too few people celebrate their choices
For building muscle stamina (since you have strength but not stamina), I'd start with the classic body weight exercises -- pushups, squats, planks, walking lunges, etc. Download Mark's eBook - it's a great start. Pullups when you can fashion a bar -- and I bought 2 tie-down straps at Home Depot and a little 1" PVC pipe and made my own "rings" (running rope through the PVC and tying the rope in a knot, then running the strap through the loop). That "system" lets me raise and lower the grip height to do all kinds of pulls and pushes.