Everyone complains about some kind of discomfort when reading from screens - I have been reading exclusively e-books for 10 years and have never experienced anything like it. But I suppose it's because the screen is too bright. Therefore, I advise you to reduce the brightness to the minimum comfortable, as well as use night modes - a black background with a font of green, white or orange. Thus, the screen practically stops glowing, and the eyes do not get tired.
Buy a device for reading e-books, for example PocketBook. It uses a special ink screen. Self-tested, ergonomic and eye-friendly.