Eye dryness. You might have developed a need for eyeglasses but the most common cause of loss of focus at the computer is eyedryness. Try using a teardrop at you convenience next to the computer.
See eye doc. Your prescription likely needs updating.
Age related. You may be starting to enter the focusing of middle age termed presbyopia in which things intermediate and near start to become less clear. It is possible the contacts you are wearing are overcorrected which will accelerate this issue. Have your lens power checked and you can also discuss with the ophthalmologist a thing called monovision which can help.