Blurry eyes could be from various things: staring at your screens too much, dry eyes, diabetes, autoimmune condition....
To rule out diabetes: Check your glucose with a glucometer. Maybe a diabetic friend has one you can use, or maybe you could spend $35 and get your own kit; or you could go to a minute-clinic or get your doctor to run blood test for A1C (3-month average of glucose). He/she probably did a blood test before your recent scoping.
Vitamin D test is easy. Many people are low. I was 25 and like 30 to 80 more normal. I take D3 supplements when I don't go out in the sun, but you have to follow up and get retested if you're doing that to make sure you don't go overboard and start calcifying your organs. <:cO
Back pain is common. Straydog listed many reasons. I tend to slouch back in my desk chair and look at a computer. And while that didn't bother before my 30s, it certainly changed around my mid-30s. If I don't slouch like that, it feels so much better. But, like you suspect it could be other reasons. You want to analyze the easy possibilities first. I got a x-ray of my back recently after 20 years of pain, and it showed no arthritis or ankylosing spondylitis (which I was really worried about). The bottom vertebra in my spine is collapsing and causing so much discomfort from time to time. I know I squashed it really bad a couple of times over the years picking up heavy stuff by myself, and then putting pressure on it with exercise and slouching. Just me.
Hope you figure it out. Analyze the possibilities but don't jump to conclusions. Keep seeing your doc if it's serious. Process of elimination.