If you feel hard emotions too often, it is better for you to be as relaxed as just possible all the time. Caffeine won't help you with controlling negative emotions, as it has the opposite effect, so it can actually cause some of the emotions you want to get rid of. So better just stop drinking coffee and black tea.
There is an article on Storyline blog written by a girl who was always claimed too emotional. Read it and you will see the non-conventional point of view and get some tips.
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