My story is very similar to you. I'm going to be 30 in just a couple weeks. I began to show signs of depression at around 13. I was dx with depression at 16. I took meds for depression on and off until I was finally dx a few years ago with bipolar. It wasn't until I was dx bipolar II and given medication for bipolar rather than just depression that I saw the difference. I found the antidepressants helped a bit, but not enough. I would seek a second opinion. Write everything down before hand. Tell them that your brother was dx bipolar II. Be very open and I hope for your sake you end up with a dx and a treatment that works for you.