Hello and welcome
I just joined these forums a few weeks ago and so far I have found it to be very helpful. There are a lot of people here who care and are willing to help out.
I came here for the same reason. I have major depression and when I get down, I can't go to family, because they just tell me its my fault and something is wrong with me. And I don't really have any friends I could go to that would really understand.
First off, I'm going to say this, there is nothing wrong with you! Don't feel anything is your fault, cause I'm sure its not. I experience some of this myself, so I can relate to what you are saying.
For me, I think it is anxiety. I get really worried about things that I shouldn't get so worried about and let things get to me, or take things to hard (grades in school for example), and I feel anxious sometimes and can't shake the feeling. I also suffer from a lot of depression, as mentioned above, and get really down a lot to the point of having suicidal thoughts. Does this sound similar to what you are experiencing?
I also know what it is like to feel alone. Being alone for too long can also cause me to become depressed. What helps me sometimes is a distraction. Finding something I like to do and getting my mind off things (music, movies, video games, ect.).
You may also be experience some symptoms of Bipolar Disorder, which is actually very common. I recently did a research paper on this for school and sudden changes in mood from being very happy and elevated, to very depressed and feeling despair are common symptoms of mania and depressive episodes.
I hope this helps you out. I know how hard it can be to be constantly worrying about things and to know you shouldn't be so worried about them, but not be able to control it. It's not a fun thing and can be very stressful.
If you need anyone to talk to, send me a pm. I hope you feel better