I’m very sorry you’re having such a hard time. I hope you are talking honestly with your therapist about what you’ve written here. We therapists wish we were mind-readers but we’re not. If people don’t tell us their thoughts and feelings, there isn’t much we can do except guess. With most appointments lasting less than an hour, we’d like to get right down to business and use the time well. It’s up to you to bring up important issues right away.
My guess is that you are still grieving your mom. Your dad is moving on before you are ready to. You feel like you’re losing him too. He’s caught up in a new relationship and is probably unaware that you are feeling left out of his life. If that weren’t enough, you are at an age when your body is adjusting to becoming an adult. It’s normal to feel moody and to have ups and downs but that doesn’t make it any easier.
My biggest concern, though, is your sleep patterns. Of course you have fatigue. Of course you are irritable. You absolutely need 8 – 10 hours sleep a night to be physically and mentally healthy. There is a reason for your headaches. It’s lack of enough sleep. It’s also possible that the “breakdown” was related to sleep deprivation. Same thing with the anxiety and moodiness and speech problems. I very much doubt that you have bipolar illness. I’d at least want to rule out all these other sleep-related issues before considering it.
Please talk to your therapist about ways to get your sleep cycles back where they should be. It’s obvious that you are intelligent and know how to research things on the Internet. Look into sleep disorders and how they are treated and you may also be able to help yourself.
I don’t know enough to comment on whether you need medicine (although I doubt it). But I absolutely do know that you need sleep!
I wish you well.