I am having memory problems, can it be a disease or medical problem?

i am 28 yrs old, i am male. I had a good memory few year ago, but nowdays i can memorize nothing, when i try to understand or read something i feel like my mind has blocked from mid of head, i cannot do a work for long time or can say i cannot concentrate for long time. it is happening with me from last 4 years.. i have remember all my memory of childhood or till 2011. after that i haven’t remember. whenever i want to study its like i am reading only not understanding. i want to ask is it any type of disease or else

Age: 28
Medications: no