I am 18. I am a Bangladeshi. I think my breasts are too small. I use 34 size bra.

Hi and thank you for your question.The best advice I can give you, is to schedule a consult with a board certified plastic surgeon to discuss your options. Best of luck!

You are still young and your breasts are continuing to change.  At 18 years of age, your breasts may increase slightly in size until your early 20s.  If you are interested in increasing your bust size, saline implants are an option (silicone is not due to your current age - at least in the USA).  If you want to avoid implants, fat transfer may also be an option.  Consult with a board certified plastic surgeon in your area to discuss options.  Good Luck!!

Breasts won't stop grown until you reach your early twenties. However the changes you will have in those few years you have left will be minimal compared to the changes you had the years prior when you were going  through puberty.
If you still feel you want bigger breast you could get an appointment with a surgeon. Also, don't fall for those creams, pills, tonics and infusions that claim they can get you bigger breasts. There are only two things that can change the size of your breasts (besides lactation) and neither of those can be accomplished by the things I mentioned before.