First of all I don't think that because you have detected a lump in you breast you need to go to the emergency,but seeing your doctor is a very wise decision.
This could be a cyst which can appear at any age, in teenagers as well as in older women.These cysts are related to the increasing hormonal fluctuations and the pain is particularly felt prior to the menstrual cycle and subside after the menses finish..
Avoiding caffeine, (Coffee,chocolate and colas) salty food and fatty food can lessen the pain considerably and minimize cysts enlargement.
The energy drink "Red bull" contains 80 milligrams of caffeine and I suppose that having 2 or more of these drinks a day doesn't help the situation.
Please don't worry or be scared..Most breast's lumps are harmless especially at your young age.
Let us know how things are proceeding and I hope that all is going to be alright.