I think that I understand what you are saying. You have been through the mental health circus and received multiple diagnosis (ADD or ADHD and Bipolar Disorder)but you are not sure that these are accurate or if you are simply faking. Also that your family believes that the ADD or ADHD diagnosis is accurate.
I can sympathize having been through that circus myself. And also struggling with exactly WHAT my diagnosis me to me and about me, as well as the internal and external stigma that comes with mental disorders. And I too in the past have often wondered if my extremely changeable moods are psychosomatic. In my case, it turns out they are not.
Here is what I suggest, make a list of all the symptoms that you exhibit. Then take it on yourself to find the answers. Read others experiences with ADD & Bipolar and see if you can relate. For bipolar I would suggest an excellent book by Kay Redfeild Jamison - An unquiet mind. many people have found her book of her own experiences, to help them in recognizing their own disorder and also accepting it. For ADD/ADHD, you may have to search a bit. I personally have not read any books on it that were biographical. Though i have heard that "Think fast - the ADD experience" by Thom Hartmann, is very helpful. There are personal stories, as well as clinical info. If you have a hard time focusing on reading an entire book, skip around and read what is interesting in it to you.
As for is it psychosomatic, I assume that you mean are you faking a condition (subconsciously) that you do not really have. The actual definition of a Psychosomatic illness is an illness that originates with emotional stress or damaging thought patterns, but has physical symptoms that are real and can harm you as much as symptoms that originate from other means.
i would guess at no. But either way, you are experiencing symptoms that are having a major effect on your quality of life and you should treat them seriously. Remember that a diagnosis is just an information label used to help us and them (docs)understand what we are experiencing and guide us in the right direction to get help. You are not whatever diagnosis you have been given. You are Matt. You may have a disorder and if so it is just a part of who you are. It may greatly affect your life outwardly, but it is only a part of you. Learning what is accurate is vital if you want to learn to improve what you can and find more stability and happiness.
Also, you mention being diagnosed after just one visit with a doc. I suggest getting another opinion. Find a new doc - i suggest a psychologist as they are more inclined to actually listen to what you are saying because they focus on therapy. My fav way is by calling potential docs after hours and listening to their message first. Do they sound concerned? Caring? Helpful? - if not they are not the doc for you. Stay away from the robotic sounding ones, they have forgotten that they are dealing with REAL peoples lives who truly need help). Once you have found one, leave a message that you want to make an appointment. When you see them, tell them your concerns. Tell them that you have been given xyz diagnosis and you are not sure that its correct. Tell them that you are wondering if your symptoms are psychosomatic. Tell them that you really want to find out the truth about what you are experiencing so that you can begin working towards a better way of handling and coping with your life. And if it turns out that you need prescriptions, then they will refer you to a psychiatrist for that. I don't recommend starting out with a psychiatrist first as their primary job is to simply medicate you, not to really listen to your experiences and perceptions. And stick with your psychologist, it can take time working together to get the accurate answers.
And try to let the stigma go. We all fear what we don't understand and mental disorders are very complex and confusing. You can't control how others feel about it, but you can educate yourself and lessen your own sense of stigma. Acceptance of ones condition is a major step in finding some balance and happiness.
I wish you the best of luck.