I think that you have the flu. It sounds like you are eating a good vegan diet, that plus the fact that you were eating very little dairy, says that it must be something else. Your symptoms are those of the flu. You can varify this by seeing your doctor. There is no way that a vegan diet would cause these symptoms unless you had a strong alergy to something that you are eating. This would be very odd since a vegetarian diet has the same foods except for eggs and dairy that a vegan diet has. So I doubt that you added anything new to your diet.