Deb.
With injections, estrogen levels can vary a lots, initially, at injection, this makes the breast grow a bit (like a women who's got her period) as the tissue expand, then when the estrogen level goes down, prolactin levels increase which stimulates the milk glands which produce a small amount of milk like substance (colustrum) which is released inside the breast which slightly distends it (thus the tension). This liquid is resorbed after awhile and the tension subsides and the breasts diminishes in size, until the next injection. For some, it gives differences of up to half a cup during their cycle, for others, the breast barely varies in size (though it may still hurt).
