Is Coffee Acidic? - and other chemistry

Question: "I am drinking a cup of coffee brewed from a French Press and made from Peruvian beans roasted by Coffee and Tea Exchange (local to me here in Chicago).  I can say that this coffee affects me differently than the coffee I buy (rarely) at work in the hospital. With my coffee at home, I don't get jittery and I don't get stomach upset. Also, I can drink a cup or two every day and I don't get a headache if I stop. On the other hand, if I go through a period where I drink a lot of coffee at work, all of those things happen. Do you know the chemistry of why?" - Howard