Sorry you haven't gotten an answer yet. I think that's because your situation is unique and I suspect that none of us is medically qualified to answer.

I suspect (but please get confirmation from your medical professional!) that you may need a pack with structure (i.e. stays) and a hipbelt which will transfer most or all of the weight to your pelvic girdle (hips). It sounds as though you want one with some ventilation in the back. Most daypacks have little structure (and often no hip belt), so you're probably looking at a small (say 30 liter?) backpack.

Nearly all packs made by the larger, brand-name companies (the kind you'll find at REI) are manufactured in Asia. About the only ones manufactured in the US are the small (sometimes called "cottage") firms that sell on the internet, not in stores. Here's a partial list (it changes and I haven't been keeping up): ULA (a sponsor here and one of the most popular with thru-hikers), Six Moon Designs, ZPacks, Elemental Horizons, Gossamer Gear, Hyperlite Mountain Gear. Mountain Laurel Designs makes lovely stuff, but their packs are frameless so probably not what you need.

I can also tell you that pack fit is almost as individual as shoe fit, and fit is the most important factor in choosing a pack. You need to pack up the stuff you're going to carry and take it with you when you go shopping. If you order through the internet, have your load ready when the pack arrives, load the pack up (keeping it clean and not removing the tags) and take a couple hours' hike around the house. Be sure to check each manufacturer's website for return policies, as you usually have only a limited time to return the pack. You may have to pay return shipping cost on several packs before you find the one that fits you!

The measurement that's important is not your height nor weight but your torso length, from the "bump" at the back of your neck down your spine to a point level with the top of your iliac crest (pelvic/hip bones). Don't try to measure this yourself (when I try to measure me, it comes out different every time!). Please also note that the pack's belt should go around the top of your pelvis, not your waist--it's to allow the pack's weight to be supported by the pelvis/hips rather than the upper spine. Again, only a medical professional can determine if this is what you need!

In the meantime, check your area for the nearest locally owned backpacking store (not a chain store) or, if none, REI, pay a visit (preferably at an uncrowded time) and try every pack they have in your size. They will measure you and you will get an idea of what a comfortable pack feels like even if none of them meet your specifications (which is what happened to me 10 years ago). Of course, you may find exactly what you're looking for and decide not to worry about where it was made!

There are several articles on choosing and fitting a pack on the home page of this site, left hand column.