Please help me...?

Hi...i hate to be talking about this, but I have a major issue with depression....whenever I try to cheer up, for some reason, a wave of sadness just comes over me that I can't overtake....the weird thing is that there is that I can't pinpoint why...is this normal? Please tell me...i wouldn't do anything to hurt myself or anyone, but the frustration that this depression causes gets to me at times....i will really appreciate kind and honest answers....thank you sooo much...