It is not a question with a straightforward answer. Some girls may feel increase in breast size after marriage (or breast massage or pressure , or regular sex) whereas there are many more who are rejected by the prospective groom because they have small breasts . Will you  go to them with Doctor's opinion that " डाक्टर ने कहा था कि शादी के बाद सब ठीक हो जाता है" ?

Hi good morning Thnxs for your question Breast tissue made up with fat and glands. Size of breast under influence of oestrogen. And oestrogen levels fluctuate from puberty to menopause. So at puberty age and reproduction age oestrogen level is good so ur breast size improves. Not related with sex. But sexual activities and massage will increase size but not significant (little) For further guidance on it Use my online consulting link so that we can discuss ur quary and advise you accordingly and guide u MY Online link is prac.to/drpanchani

Not very appreciable change

Will not May increase after lactation

It can increase, but theres not gonna be drastic change.