It is difficult to give you a diagnosis. It is possible that you have PTSD. PTSD generally occurs after a trauma. Your negative experiences with mental health facilities have caused you great distress and may explain some of your symptoms.
In addition to PTSD you may also have a general anxiety disorder. Again it is difficult for me to know with certainty what your diagnosis is. The best way to know your specific diagnosis is to have a complete psychiatric evaluation. Even then it may be difficult to gain a specific diagnosis, at least in part because you are taking multiple medications. Medication, for some individuals, blunts their emotions and sometimes makes it difficult for them to feel. Medication may also explain why you feel a sense of detachment/derealization/depersonalization.
It must have been difficult for you to have experienced what you have. You may not have any specific diagnoses. You may simply be reacting to your difficult life experiences. You began your letter by describing yourself as the scapegoat in your family. You believe that you have disappointed your parents. I get the sense that you “never felt good enough.” The negative feelings you have about yourself most likely contribute to your everyday suffering. Therapy could assist you in sorting out your feelings as well as to help you examine the truth about your place in the family. You may feel as though you failed your parents but that may not be the case. Just because we feel that something is true does not mean that it is. The way you feel about yourself and your place in the family is something that should be examined objectively.
You’ve been sent to various facilities by your family. Maybe the problem isn’t you per se. Maybe it’s the family who needs to learn a new style of interaction. Family therapy may be helpful with this.
If you’re willing you should also consider individual therapy, in addition to family therapy. You may have had individual therapy in the past and it may or may not have been helpful. Even if you have had prior individual counseling I still believe it could help you now, especially if you had a very good therapist.
I’m sorry that I cannot offer you any definitive answers. It is always difficult to give a diagnosis over the Internet. I hope you’re able to find help so you can finally put together the “missing pieces” of your life’s puzzle. Don’t give up. Here is a link to a website you can review and find local therapists. Thank you for writing.