u should see your doctor. you don't need to feel this way. I went through it and it really sucks but my doctor put me on medicine that really helped and I don't feel that way anymore. good luck and I hope u feel better soon : )
Sometimes people do need to see a doctor. But sometimes it is physiological; people need protein to maintain stable chemistry. For instance, If my teen daughter is cranky, I give her some cheese and it helps within minutes. But, you know, sad is a normal part of life, and it's OK to be sad at times. Even right after feeling happy. If you feel that the sadness is overwhelming, or are scared that it won't go away, then please speak with someone.