A; You’re right. At your age it’s hard to know if this is about adjusting to adolescence or if there is something more serious going on. Whichever it is, it’s important to take it seriously.
The first step is to see your doctor. I’m concerned about the sleep disorder. If you aren’t getting a good solid 8 hours or more of sleep every night, that may be a major source of your problems. Fortunately, there are ways to help you get better sleep. Revising your routines and learning ways to relax can help a great deal. If you are still having difficulty getting to sleep or staying asleep, your doctor might prescribe some medicine to help you get back into a reasonable rhythm.
At 16, you may also be dealing with some hormonal shifts that are creating the ups and downs you describe. As with the sleep, your doctor is the place to start.
If everything checks out medically, then I suggest you consider seeing a psychiatrist. Since your life is generally fine, it may be that you are having the mood swings that are symptoms of either an organic depression or bipolar disorder. In that case, some medicine coupled with some counseling to help you learn new ways to manage your feelings is the next step.
You are fortunate to have supportive parents and friends. I’m sure you will get through whatever the trouble is if you get the consultations you need to identify the source of your distress.
I wish you well.