What's going on with my memory?

im 18 and i use to be able to remember everything.well, a lot more than others. If i was to take a spelling test the next day, i would just look at the words for 5 seconds and boom i knew how to spell it. i can't do that anymore! i have to write them several times. i never had to write down my homework ignments, id just look at the board and memorize it. now i have to write them down or i forget. i use to be able to memorize great details. for example, my friends don't remember what they were the other day, well i can remember what my niece wore last sunday. i use to be able to remember what was happening in the background and people's facial expressions. when i studied for a test all i really had to do was look at the paper. i would just remember the order of the paragraphs, the placement or words, and if something was underlined. im 18 why is this happening to me?