Energy Lag + Green Tea = Stomach Ache

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So I'm lacking energy from time to time, definitely a sign I need to tweak something that I'm eating (and I'll be working on that this week!) BUT I drink green tea (Lipton, made with a tea bag, brand new box) from time to time as well because I read everywhere that it's great for diets and energy. They're not lying that it's great for diets - I drink green tea and I'm nauseated for several hours after! Anybody else get this? I don't know what it is, but I do not get the same reaction when I drink black teas (which evidently aren't as good for you as green tea?), so I want to just drink black tea and be done with it, but I also want to make healthy lifestyle choices to improve upon my quality of life.

Anybody got any guesses/remedies? *Drinking black tea with breakfast as we speak...*