Your childhood sounds a lot like mine. Only I am to this day an only child. Your teens were very different, I didn't drink or have sex or even date... however I was shy and people thought I was a snob because of it. I saw some creatures in my room as a little girl and sometimes heard the piano playing when it wasn't. When I graduated high school I decided I couldnt' stand my low self esteem and I hated myself so much I wanted help. I too was diagnosed for several years with depression (plus OCD which was accurate... but that's another forum altogether). A lot of us are misdiagnosed with depression because we see our doctors when we are depressed and often avoid them when we have our "up swings". After being depressed, being manic can actually feel pretty good so we often think we are "doing better" when it is actually a real symptom. After three years of trying different meds and therapies my psychiatrist decided that maybe something else was going on so I was scheduled for regular visits -once a week - so she could evaluate me more closely. That is when she realized I was actually bipolar, not depressed and since then things have gotten so much better. I don't understand all the technical stuff dealing with our disorder, but bring the possibility up to your doctor so she can take a closer look at your behavior. It is a possible diagnosis, and once you have the proper diagnosis, you are on your way.
PS Do not be afraid of medication... if you were diabetic you wouldn't think twice about taking your medication regularily... psychological disorders are phsyical, chemical disorders and often require medication as well. People don't always realize that the brain is part of the body and can get sick just like any other! Best of luck!