Oh wow OP, your life has been very traumatic from the beginning. Your anxiety likely is caused by this trauma, it is a key symptom of cPTSD- complex Post Traumatic Stress Disorder which is a type of PTSD people develop when they have undergone long term serious trauma.
Not fitting in anywhere - that’s honestly not unusual for someone that experienced such trauma and was parentified as a child. You were never parented because your father died at an early age and your mum was an unavailable alcoholic. Instead you had to parent yourself and your brother. You can’t relate to most adults who had a ok childhood and a proper child/parent relationship.
The cousin raping you- that’s not your fault, I am so sorry you feel ashamed of it. You shouldn’t. You were a vulnerable child with no present parents and these older boys/men took advantage of that.
You have been let down & traumatised by every adult or person that was meant to love and to protect you, it is only natural that your personality would then be hyper cautious of other people, especially those who say they love you. Your anxiety is literally what you need to survive. To try and avoid being hurt again.
Your doctor is crap. Is there anyway you can see a different GP? And ask them about a psychological assessment? Perhaps some therapy for cPTSD? This isn’t a regular anxiety disorder that can be helped with a few pills. You need some one to one, long term, intensive therapy.