I am very concerned about what you shared in your letter. The first thing to do is talk to your therapist about how to report the assaults by your cousin to police. You should not live under the threat of further abuse. You deserve to feel safe in your own home.
The sleep disorder then needs to be dealt with: It may be at the root of at least some of your problems. As you know, a sleep disorder can cause sleep walking, sleep paralysis and even the sense of strange presences. If you aren’t getting 8 – 9 hours of real sleep a night, that may explain at least some of your symptoms.
Medication alone is not likely to be helpful. Getting your sleep regulated will take some real effort on your part. That means creating a sleep schedule and sleep routines that are conducive to getting to sleep and staying asleep. Don’t drink any caffeine after noon. Don’t nap during the day. Get off all screens at least an hour before bed time. Then do something that is calming and relaxing. Settle in for the night. If you don’t fall asleep within an hour, don’t toss and turn. Get up and do something constructive (like homework or cleaning). Try again to go to sleep. If that doesn’t work, ask your therapist to teach you some relaxation techniques.
You are less than a year from adult status when more choices will be available to you. I hope you are preparing for the life you want. Do well in school so you have the option of going away to college. If that doesn’t seem possible at this time, make sure you are developing some skill that will allow you to get out on your own and support yourself.
Do talk further with your therapist about your sense that she doesn’t believe you. I suspect there is more to it than your age. It may be that she has formed an impression that you need to correct. It may be that you aren’t reading her correctly. Discussing your concern may be an important turning point in your therapy.
I wish you well.