Do you know why are you sad? If you can go and help a stranger with any small thing you can, but not just giving money. Small things mean helping and old person cross the street or offer to pick up their bag etc. You will feel different. Remember helping means no hope of returns. Help and walk away. Try to keep I, me and mine out of the picture, meaning do not feel or say i did this and that, just walk away.
Let us know if this helps. If you can eat a few organic apples a day that also will help you. FASTING WILL DEFINITELY HELP.