Cylinder power 0. 75. Power cause pain!

Sir my age is 20 years actually in July I got eye checkup then my power is 0.5 cylinder in both eyes and 0.25 spherical in both eyes now last month in December I again go for eye checkup then doctor check and told no spherical power needed vision is improving but cylinder power is 0.75 I asked why cylinder power increase he told you are 20 year old eyes are still developing so cylinder power will changes it is normal for cylinder power to change little bit and i have dry eyes also he gave me drops for dry eyes my question is even though I am wearing specs but when I watch mobile for long hours my eyes and head pain actually if I tell you the pain is just below eyebrow in that area below eye brow there is pain and radiates to forehead i wear glasses whole day and watch mobile please tell why area below eye brow is pain when I watch mobile even though I wear specs whole day can it  because of specs as I wear it whole day so that area pain or what please tell do cylinder power cause pain