Some research facts which might be of help

[TigerPaws]

I have researched the mechanism (hormones) and the reasons as well as the sources of breast growth as well as the growth cycle.
While the results below are by no means complete here are a few of my findings.
Fundamentally there is no difference between a man 's and a women's breasts. When properly stimulated by Estrogen, Progesterone and occasionally Prolactin a man will develop breasts.
The reasons for elevated  hormone levels are varied, external chemicals (medications), physical such as loss of the testicles, genetic, a pituitary gland tumor (Prolactinoma) which can dramatically increase Prolactin levels and suppression the sex hormone binding globulin (SHBG) which can come from many sources.
The size and occasionally the shape of a man's breasts are largely governed by genetics, if you want to have a general idea of how big you will get look at your mother, maternal grandmother and any sisters you may have. Weight will make a difference in how big you are, not in the size of the breast gland (that is governed by hormone levels and genetics) but in how much Adipose fat (fatty tissue behind the breast) you have. Loose some weight and your breasts will not show as much.
The attached image gives a fairly good representation of the internal structure of our breast and if you look carefully you may have a better idea as to why your breasts hurt when they are in a growth cycle. There is a great deal of underlying structure in your breasts and where they are growing and expanding into the surrounding tissue it hurts and itches.