Or buy a copy of each text to use at home.
Easier said then done. Most K-12 students don’t actually buy their textbooks, the school issues one per student and they turn it in at the end of the year. Some schools don’t even have enought to do that. Where would parents buy extra copies of them? Directly from the publisher? 
As for college students where would we keep textbooks other than at home or in a dorm?
One of the things that makes a big difference is gentle full range-of-motion movements. Most of us don’t get enough motion in our shoulders and neck, what with sitting in front of a computer, standing at a sink or cutting board, etc. Several times a day, just reach up like you’re going to pick bananas.
A little harder to describe but even better: raise your elbows as high as you can and draw them as far back as you can, arms bent. Then rotate your wrists so your thumbs swing down and end up pointing out to the sides. Take all of those motions to the limits and hold it for a while, maybe 15 seconds. Do that several times a day. You’ll really start to feel it working after just a couple of days.
But WhyNot is right: if the problem is chronic you need expert treatment. A really good physical therapist can provide a proper diagnosis and treatment plan.