My girlfriend is 19 and I noticed that her breast is smaller than other girls of her age. I'm scared that it can be because I often play with her breast. I suck them and even pressing them, sometimes she says that it hurts. Since last month I thought about stoping it, but when I'm excited I just CAN'T!
I need an expert advice who knows such informatin, should I stop? It will make her problems? 
Hi krazy008, I'm not an expert but I know something about it so I might be able to help you.
There are certain things that can increase breasts like getting older, weight gain, pregnancy, playing with them it won't have any influence on their size. Also these sexual play like sucking and pressing them won't cause any troubles unless you will press them harder enough to leave it purple or blue. Anyway, I don't think your girlfriend let's you doing that cuz', logically, it hurts. If you both like this kind of activity it is totally normal and you can keep it doing further. Just make sure she wear a good bra which doesn't tighten her breasts.
Good luck and have fun you two 
I am glad you care about her health
P.S: There are some breasts exercises, she could try them to be in shape.
Thanks man for your response, now I'm feeling much better since I don't make her problems with that. I'll just take care not to hurt her while playing, also I will tell her your advice about breasts exercises and to pay more attention to what kind of bra she wears. Have a great time and many thanks for your sharing 
Hello krazy008, I see that some days passed since you wrote your post and now you already found out what you needed, but maybe the information I will share here will help your girlfriend, so you can let her know about it.
I agree with MBernic that unless you press or squeeze it very hard you won't harm your girlfriend's breasts, but I want to tell your girlfriend the way she might protect her breasts. She need to have a good regime to stay at the correct weight (every woman has her own) and she need to be in a good fit. I want to warn you that repeated cycles of diet can cause great damage to her breasts and have the risk of gain much unwanted weight, which also can cause damage to her breasts. Also exercising is very good, but she needs to wear a good fitting bra when doing it, protecting them from bouncing and stretching. There are some periods when breasts can enlarge a little bit: during ovulation, menstruation and sometimes when taking birth control hormones (and of course when pregnant).
For more information you could add me and we can talk if you wish. I will be glad helping you guys.
heeeey every oneee i have a question tooo, my boyfrend is also crazy after my boobs he really luves them, to play wit them, to press and to suck my niples, i looooooove it too, i really enjoy it and i get so turned on when he is doing it, but i do hav some pains when he is pressing them or sucking tooo hard, i wanna ask if this is oke or i can have some problems becuz of it? i need to know plizzzzzzzzzzzzzz help me
Hello there, if you have some pains while he's playing with your breasts then ask him to play a bit softer because pain is never fun. I would recommend you to show him how to play with them and how to touch you. Show him and talk to him step by step because a men does not get born with all the knowledge about a female body. If we women do not teach them, they will never know because they don't feel what you're feeling. Remember that even if he had other girlfriends he can't feel what you're feeling. Maybe you have a spot giving you more pleasure and he doesn't know about it, or you have a weak spot where you can be easily feel pain and again, he doesn't know about it. Every single woman is different from each other so I recommend you to teach him what you like, how to press, how to play and in general everything. I mean not only in bed. Also follow some recommendation written above. Wear a good bra, a bra that fits you and keep your weight correct for your height. I wish you to be happy and pleased, my best!