My shoulders actually hurt me more in my younger years. Then in my early 30's I started weight training and it really helped. I think women on the average have less upper body strength and more shoulder pain than men on the average.

Also, think about what you are wearing. Shoulder straps can rub you raw if you go sleeveless, or hurt if you have lumpy clothing under.

The shoulder blade ache may be due to your pack pulling you back. This happens when the center of gravity of the pack is not over your center of gravity. Put the heavy stuff as close to your back as possible. Also do not dangle stuff off the back of the pack. If your pack has compression straps, use them to squish the load into a more narrow profile.

I carry almost all my load on my hips by really tightening my hip belt. I alternately loosen the hip belt to relieve my hips and carry the weight on my shoulders.

Also, relaxe when you walk. Beginners are usually way too tense and that causes pain. I also find that short rest breaks at regular intevals are better than long rest braks at longer intervals. I usually do 50 minutes walking and 10 minute break.

I still hurt from my pack at the begining of the season. By the second or third trip it is much better.

A cheaper pack is not necessarily bad as long as it fits you. You can take it to REI and they will evaluate the fit for you.