It sounds like you have a solitary quality to your personality. This is okay but ask yourself if this is a result of low self esteem. If you just have trouble making friends that is fine but if this is a response to low self esteem then you may want to address that. Sometimes people find connecting with others difficult when they don't think highly of themselves. You should try to have some social contact that you enjoy. You have to find out what this is whether hobbies or interests. A class is a good idea but there are other interests. You can also consider seeing a therapist to work on your communication styles and the fact that you feel isolated or disconnected from others. This can be related to some issues in how you feel about yourself.
Some of this can be related to your place in the grief process. You could meet with someone to figure out if missing your mom is part of feeling that you are not heard. You may be relating to others as part of your grief.
If this is helpful press accept
I'm not sure if it is related to the grief process, although that hasn't helped the situation along. My "aloneness" has been with me for as long as I can remember.
I was quite solitary as a child, though I had my mother's attention until my brother was born when I was five. But he was born with health problems and I lost her attention almost entirely after that until, I suppose, I became old enough for she and I to become close "friends".
I don't know about the hobbies and interests thing - I've tried those and whilst I have been with people with a shared interest, it has never developed into friendship.
Sometimes, I get fed up about being me and would be quite content to be properly alone, except that I have to function in the world of people for as long as I have to work and it's getting me down that it isn't working out.
It is okay to be a loner. That is a personality style that some people can be content with. However you need to find the happiness that comes with functioning in the every day world. That means that you need to find comfort and security in a certain degree of interacting with others. You can do that work in a clinical setting. You may also seek to resolve the feelings that you were left out when your brother arrived. Don't pressure yourself into a huge amount of contact just try to find the happy medium. You may find one day that some of these contacts are more pleasant. You have to leave your comfort zone a little to really be able to interact in your professional world. I would push myself in the idea that I can interact and let people come a little closer.