It might be worth having a medical / dietary check-up to see if there is a specific physical factor afflicting powers of concentration. Many people find, for instance, that whatever benefit they get from caffeine and sugar in terms of keeping awake, they pay for in terms of having "a grasshopper mind" and not being able to concentrate on mental labour.

You don't mention what age you are or what your sleep pattern is. But at any age, sleep deficits will play havoc with cognitive achievement. This is why despotic governments have traditionally placed such a high emphasis on using sleep deprivation as a means to torture prisoners.

I speak as one whose powers of concentration are much weaker (and always were much weaker) than people would expect from my general intelligence, such as it is, my literacy, and my ability to speak in grammatical sentences. Any mental disorder, be it anxiety or unipolar depression or bipolar or OCD or what not, will impede concentration. (Anxiety and OCD are my two most severe disorders.)

Just a few suggestions that you might want to consider. I can't imagine any doctor objecting to you wanting a check-up of the sort that I've described.