Is it normal to have stretch marks and saggy boobs at 12 years of age?

I am sorry you are embarrassed by your breasts at this (early) time of your development. Stretch marks are not due entirely to mechanical stretching, but can also be partly due to rapid growth, weight gain, and even in perfectly slim young women, by hormones gone wild. Yours are certainly surging as you are going through puberty.There are lots of "snake oil" treatments for stretch marks, all of them basically worthless (except to the person selling them). Laser, micro-needle, or RF (radio frequency) treatments have been shown to have limited benefit for some patients, but I would recommend waiting until your growth and breast development is complete.Plastic surgical procedures can give you prettier and fuller breasts once development is complete, so you have a few years to research the perfect plastic surgeon for you. In the meantime, realize that you are not alone with breasts that don't have the appearance you like, and that they can be made much much better. Develop a tough mental attitude, don't let self-consciousness limit your social and personal activities (I know, easy to say, tough to do, but that's up to you), and don't blame your parents. They got their genetics from their parents, etc. Work on what you CAN change right now, like stay active, slim, involved with friends and sports, study hard, and know this is absolutely correctable! Honest. And, click on the web reference link below--you may be interested in a couple of my patients shown. Best wishes! Dr. Tholen

You should discuss your concerns with your pediatrician.  If appropriate then he may refer you to a plastic surgeon.  More than likely you will need to wait until your breast growth is stable for at least one year before anything can be done.  

Your mom is correct. It is just the way you have developed. You would be surprised at the very wide variety of breast size and shape there are in your peers. At an appropriate time, consideration of a surgical procedure to improve your situation is an option.