tbf yea you should be pround but only if you actually like them surely. you can get creams and stuff for stretch marks and as you said if you wearing a bra thats comfy and fits then that cant be a problem. guys may not care but if you feel crap about yourself then things might not work with other people, you need confidence about your body. sagging breasts are due to the ligaments and the skin stretching and even surgery has various results, try creams and new bras and try and gain confidence .
everyone has something they hate about them selves.