I used to take concerta in university and in the early years of my career. i stopped taking it and its been 2 years now since ive been off it. im currently finding it impossible to focus, particularly with working from home. should i start again?

Time for evaluation: People perform at their best when they get adequate sleep, have proper nutrition, are free from illness &work in a comfortable environment. You need to write down any and all symptoms you have, time they started, things you have tried, etc. & schedule an evaluation with your doc. A sleep study may be indicated as would blood tests & a physical. That visit can begin your path to success.

Quite likely: It seems you have had ADD (attention deficit disorder), which often extends to adulthood. I would recommend to resume taking stimulant such as Concerta or Adderall XR at least on your workdays.