My guess is that your mom is trying too hard to be both mother and father to you. She has lost her husband and partner and is trying her best to raise a boy. It’s not easy. If she goes overboard, it’s because she loves you and doesn’t want to lose you to alcohol like she lost your dad. Please try to walk in her shoes a bit. That doesn’t mean I think she is totally right. But it often helps to see where someone is coming from if you want to have a useful conversation.
Now — as far as the art is concerned. You can practice and do well in school. Most good art schools expect good grades as well as a portfolio. If you really want to be an artist, stop complaining and start working on it. Go to the art teacher in your school and find out what you are going to need to do to make a portfolio for when you apply to college. Set aside an hour or two a day to perfect your drawing skills. I’m sure the art teacher will give you some exercises to do that will help you improve. And concentrate on bringing up your grades in other subjects, too. You won’t get into a good school that has a solid art major with wishes and good intentions. You have to put in the effort.
As far as making friends: Lots of teens have the same issue. It’s painful to feel alone. It’s easier to be depressed than to do something about it. But sitting in your room feeling bad isn’t likely to bring people into your life. I suggest you join the art club if there is one at school. Get involved with some charity that attracts student volunteers. It’s easier to make friends when you have a project in common. See if the art teacher would be interested in sponsoring a public mural or some other project for the creative kids you know. Focusing on the project takes the pressure off new relationships. Working on something together often is the basis for turning acquaintances into friends.
As for your weight: Well, that’s also something you can do something about. Start walking every day for an hour. Ask your mom to help you plan nutritious and filling meals. Focus on getting healthy, not on dieting (which can make a person feel deprived).
In short: You aren’t going to fix anything by sitting around wishing. Make a self-improvement plan and work on it every day. Start by listing the things you have going for you. I already know two: You have a mother who loves you and you have art talent. Those are the foundation on which you can build your future.
I wish you well.