Doctor Appointment about Back Pain

Finally got a doctor's appointment to discuss my back pain, or any good recommendations how to proceed with exercise. See, the last doc I saw (for a different condition) said forget about walking and cardio; do strength training. So I've been attempting to use my wimpy weights and do these other little supposed activities with words like "sculpting" in the description. While anything over 5 pounds does cause tension, it was the stretches that really knocked me out. So first off, doc said don't do any weights; just walk. Sure, whatever. Cant make all the docs happy all the time. We discussed physical therapy, and decided on trying a sheet of recommended exercises first. Starting very small: 2 exercises the first week, only 1 rep per day, gradually building up. Then add two more exercises, and so on. Only odd thing was the idea of 20 minutes of exercise 3x a week being sufficient. Uhm, if we count strengthening, I'm doing the total amount for the week or more. So what's up with such a tiny goal? Is that only for beginners? Worth a try, I guess. He also gave me a prescription for pain if/when it gets super bad (non-addictive). That's at least a resource so I can sleep or concentrate or get throught when I accidentally trigger something.