Hi Leyton. I am so sorry for what you are going through. My brother died one year ago today. It was unexpected.
Feeling lonely, mad, and not concentrating are normal as you grief. For me, I needed to do stuff to remember my big brother. I designed a necklace; my parents got tattoos! I have 4 additional siblings and 3 also got tattoos! We also made a garden at my parents' house. You need to remember him-- the happy time. The great memories. You will be exhausted in the coming days. and then it will get better. I promise. Then, you will get exhausted and mad again.
One thing you can do, write letter to your brother every day or when you feel you need to. Just put them in a box. Read them later.
Every first-- his birthday, your birthday, holidays, -- will be tough. The day before and the day after just as much as the day of... always plan stuff even if you don't do it.
I have support of some great siblings and parents and I hope you can find some too. Check out http://www.compassionatefriends.org for great resources and maybe there is something like that where you are.
Many hugs to you as you learn to deal with your 'new normal.'