Hi. I've been where you are now, as have many adults, so try not to get too worked up over this. It's more common than you might think and even some of your closest school friends may be going through this right now, just like you. The trouble is, we all try to hide these feelings, try to look 'normal' and act normally - even though we feel like we are falling apart inside.
First things first ... tell your Mom. Even if you can't sit down and tell her face-to-face, why not try writing her a letter to explain how you feel and what's been happening to you. The last thing she will want is you feeling dreadful, so the sooner she can get involved and offer her support and help the better. You can hand her the letter or just leave it for her - and once she's read it, you can both sit down and go through things properly. Believe me, this is the best thing you could do.
It is very normal to feel tired and depressed when you are 13 years old. Your body is going through a huge number of changes and this has an effect on your neurological system. It affects how you think - and (this is important) it is temporary. These feelings will pass. But right now you need some support, some empathy from those that love you and maybe (worth asking) some sup[port from your school counselor. The fact that you don't know them is sometimes better, because they won't pre-judge you, they will just offer their professional help.
Hoping this helps. Be brave - tell your Mom what's happening. You won't regret it.
Tony
You are not alone. The good thing is you know what's causing your anxiety. Telling your mom will take a lot of the pressure off of you. You say your mom is a loving mom. You just need to sit down and tell her everything you just told us. School and friends can be hard growing up and a once straight A student now might be a c-d student. Your young and and have your whole life a headed of you. If you need to talk to the student counselor that's what you need to do she would be able to help you with the school work. But telling your mom and getting it out willake you feel better in the end. Good luck honey it will all work out. Moms love there kids and only want the best for them