Male, one breast larger than the other.

Gynecomastia is caused by excess breast tissue and fat. Pseudogynecomastia is caused by fat only. Most men have both breast tissue and fat. In some cases there can be pain associated with enlarged breasts, or there may be other causes. You should see a Board Certified Plastic Surgeon who specializes in gynecomastia to evaluate your situation and give you recommendations. Good luck.

It sounds as if you have gynecomastia. Since you are 18, you are old enough to consider surgery to fix the issue. Schedule a consultation with a board certified plastic surgeon to be examined in person and discuss your options. There is no reason to live with this if you don't want to.