Wow, you have challenges I haven't considered. But good work. You will get better with practice!

Long ago, I lived on the 4th floor (three flights above ground floor) of a building with no elevator. I used my bike for everything. I had a big milk crate on the back of my bike. When I had a heavy load of groceries, I sometimes carried the whole darned thing up the stairs, and I sometimes made two trips. Neither approach made it easy. But I got strong. I didn't carry water, but I did carry cat litter, also heavy.

And speaking of that, I live on the 4th floor now, and major elevator renovations start tomorrow. We will be elevatorless for the rest of the summer!

Here is another tip: always take stairs two at a time. That's what I do, even when I'm carrying heavy stuff. It builds strength. I took a few years away from the bike, and when I got back on, I was still strong, because I was climbing a lot of stairs two at a time. But you live in Texas. Do you have stairs?