I am sorry that you are struggling. In some respects, what you have described is normal for a teenager but there is also clear evidence of the symptoms of depression and anxiety. During your high school years, it is normal to struggle with self-esteem and identity development issues. Developmentally, you may be experiencing the “identity versus identity confusion” stage. This stage generally occurs during one’s high school years. At this life stage, individuals are attempting to find their own identity. It typically involves trying to fit in with other people, joining new groups, etc. It is essentially a time of trying to determine who you are and where you fit in. It is a normal, healthy and necessary stage of life.
Your obsession with having a particular disease is not a normal part of this stage. That obsession is a symptom often associated with anxiety, specifically obsessive compulsive disorder (OCD). This does not mean that you have OCD but it is a sign that anxiety is a definitive presence in your life.
Having “cloudy” thoughts and feeling as though you have “no personality” may be side effects of antidepressant medication. It is not uncommon for people who take antidepressant medication to report that they feel numb or lack a normal range of emotions. Some individuals report that they have difficulty with concentration while taking antidepressant medications. In many cases however, it is difficult to distinguish between medication side effects and psychological disorder symptoms. Even so, you should check with your prescribing physician to assess the possibility that some of your symptoms may be caused by medication side effects. In addition, be sure to discuss those and all other symptoms with your new therapist.
I am glad that you have made an appointment to see a therapist. You are taking a proactive approach in dealing with your issues. From my perspective, you are doing exactly what you need to be. One additional recommendation I have for you is to educate yourself about anxiety disorders and low self-esteem issues. You can accomplish this by reading books, reviewing websites, talking to other teens, or joining support groups, (online or in-person). I wish you the best of luck. Please take care.