I would suggest researching Breast Massage and Fat Transfer massage, there are many youtube video's and other sites dedicated to Japanese - Thai breast massage for growth.
Considering you still right in the middle of puberty and your naturally high levels of Growth Hormone and a bunch of factors, you might find if you are diligent about it and do it every morning and evening non-stop for 15-30mins per day.. you might find you able to grow another cup or 2.
Ensure you are getting enough mono-saturated fats, considering eating green papaya - not ripe ones (digestive enzymes in green papaya may help) and ensure you getting enough collagen in your diet (chicken feet soup, beef knuckles stew, fish bone soup etc.) to aid in building of different mammary glands etc.
At your age you are primed for growth, you don't need herbs and phytoestrogens unless you have been diagnosed clinically with being low in estrogen, high in testostorone or low in progestrone. However, if you're a b-cup already.. you probably dont have a hormone issue and just need to motivate them physically to grow a bit more. If you are really concerned and can afford to do so, you might want to get tested for a female panel via saliva testing. Would cost about $200.
Are you on birth control - if so, which one as each type affects hormones differently.
What shape do you have? Have you looked into tuberous breasts and also the Tanner staging system - both breasts and pubic hair? That should help you see if you are delayed at all but by the sounds of it, you have no reason for concern.
Here is a link in the Merck manual that shows the tanner stages.
Tanner Stages of Puberty Development for Females
When you have had a look, let us know more about where you are at, your height, weight and what you typically eat and we'll see if we can guide you in a direction to help you grow a bit faster... if you really feel you need to.