Having blurry vision. Taken 3 months.

Hello doctor, I have been wearing glass for nearly 12 + years for short sight and now my eye power has increased to - 5 on both eyes. For comfort and clarity I am using lens for nearly 6+ years . In recent times I have issue like sudden darkening of eyes accompanied with giddiness and nowday I feel that my eyes are more blurry and since I work on computer I find it hard to concentrate of words . I still couldn't come to conclusion whether it is because of the lenses I use or the eye itself is making some problem . End of the day eyes are tired and feel only like closing and sleeping to wake and feel little releived . Pls. Suggest what needs to be done , since to recoganise this problem I have taken 3 months . Thanks in advance for your suggestion . Regards, Mohan