What Causes Poor Concentration With Slurring Of Words?

Hello, latley I've been having trouble writing. I'm a 21 year old student and we are required to write alot of essays, research papers,... but over the last few years my ability to write has diminished. I had no problem writing back in highschool or even in my first year of college. Now, three years later, I can sit infront of the computer all day and nothing or very little comes out on paper, I struggle(as i do now as im writing this) to put every sentence on paper. In our writen exams most students write at least a page and a half or two if not more, I only get about 3/4 of a page(in my first year i could write up to a page and a half). My profesor says that I anwser all the main points and i anwser them correctly but in a very reduced way. Another thing that might be connected to this is I forget words frequently, I might be having a conversation and all of a sudden I forget the word i'm about to use, I know what it means, i can imagine the object or whatever in my head but i dont have the word for it. Then i shoot a few similar words out till i get the one i want. Or I might remember the word in another language and use that.
One thing that might contribute to this problem is that i dont use language that much Im not realy a social person and i dont talk much per day. But I've been equaly social in highschool and I didnt have this kind of problems and i read more books now than i did back then. I'm really affraid there is something wrong with my brain, so I ask for your advice. Lately i started reading alot and doing all sorts of brain exercises but there is no improvement.
(btw it took me well over an hour to write this)