My breasts are quite small so there is not much fatty tissue there. i am also slightly overweight. if i lose weight will my breasts become smaller?

Unlikely: If you lose weight it will mostly be due to reduction of fatty tissue; since you don't have much in your breast it's likely that it will not change much with weight loss. It sounds like you might be concerned about having small breasts; while popular culture puts a premium on big breasts, many people find small breasts attractive. That said, the herb puereria mirifica can increase breast size.