Hi Belladonna
Looks like your post got missed due to the hols - hope you haven't despaired of anyone answering!
I can't really help much here - but just to say I used to get mastitis when breast-feeding my babies and it used to affect one breast especially, and also before this I used to get breast pain in one particular breast, and mine are also different sizes - so I imagine depending on a variety of factors they may or may not both react in the same way.
Yes changes in hormone doses and levels ( both of progesterone and oestrogen) can cause pain and temporary swelling in breasts but it is always worth getting symptoms checked out if you are worried.
Do be sure also to check your breasts regularly so that you get to know them and always be alert for any lumps and bumps, especially something new.
Let us know how you got on with your appointment?
Hurdity x