Can you tell me how I can lose weight and why do I still have gynecomastia?

It may not be fat. If your gynecomastia is more due to excess glandular tissue it will have no relationship to your weight and is solely under the influence of hormones or hormone like substances. Surgical excision is probably the best option in these cases and it is best done by a plastic surgeon.
Depends on the cause. Gynocomastia can arise on its own or can be secondary to certain drugs (ie marijuana and many prescription meds) and also can be secondary to hormonal problems that may signal a bigger issue. Consider seeing your md for help with a weight loss plan. If you do have gynocomastia, you need a testicular exam, review of your medications, and several blood tests that are not part of routine bloodwork.