Help? Suicide won't leave me alone...?

I'm a 15 year-old female, and I have a great life. I have always been that girl, the well-behaved, kind little angel with perfect grades and witty jokes who is always smiling and happy. I am expected to keep up this mask constantly, regardless of how I really feel. I have, for the past year and a half (or so), been fighting off recurring thoughts(and sometimes nearly attempted plans) of suicide. I can't find any reason for these thoughts or the depression and rage that have overtaken me. My father is a doctor so we're well off, and we have an excess of pills in the house. I don't know what to do, and my focus on school has kept me from making any real, trustworthy friends. Please help me.