Hello Doctor... I Have Myopia From 2005... I Checked My

Hello doctor... I have myopia from 2005... i checked my pleyes seven months before.. my power was 3 on both the eyes.. i preferred to wear lens.. but i dont know any knowledge about lens... as months went on.. i couldn't see thhe distant objects clearly.. so i thought some problem in lens so i wished to change my lens.. yesterday i went to hopital and checked they said my power has increased to 4.5.. what is the reason for this sudden increase of my power.??