[jyl]

You're just starting to get back in shape. Don't be impatient with yourself. It will come.

Make sure your saddle is high enough. If your legs are not fully extending at the bottom of the pedal stroke (just a slight bend at the knee, and a slight point of the ankle), your knees (quads) will be exhausted quickly. Just like waddling in a duck crouch is exhausting.

Start out using lower gears. Learn what 80 rpm feels like, and shift to keep your cadence at that level or higher. Pushing high gears with a low cadence will exhaust you quickly, and is tough on the knees. That applies when you're working - for just lazily gliding along, a low cadence is fine.

Just ride every day, or as close as you can. As you get fitter, you'll get lighter, and as you get lighter, you'll climb faster.

Riding on busy streets - you don't have to. I've been riding on city streets since I was 7 y/o and exploring downtown Vancouver B.C. on my little bike. You get used to it. I don't think it is any more dangerous than riding a motorcycle. Actually, fatality statistics show cycling is a lot less dangerous than motorcycling. If you're careful and very alert, I think both are reasonably safe, by my standards anyway.