I feel like i'm unable to focus as well as my grades have gone down. i've never been like this?

Basics: A person performs at their best when they are healthy, get proper sleep, get proper nutrition & in a comfortable setting. You need to examine each of these main issues for the most likely problem. If needed have a checkup to make sure there are no health issues contributing to this process. Stress is another factor you may need help with.

Can see Pediatrician: Doctor can help. A teen who wants to have better focus and memory, such as for school, can do some simple things. Get healthy (get rid of any aches, pains, stiffness, or tummy gurgling). Avoid any drugs like caffeine, nicotine, alcohol, or over-the-counter sedating or stimulating medicines. Sleep enough and properly (same daily schedule). Maintain a happy mood (avoid anxiety, fear, sadness, etc..)