Overall weight, hormones, and medications. I remember my elderly Mom complaining when her bra size increased following a medication change (possibly a blood pressure med).
Yup - i'm the fittest I've been in years, definitely not fat, or even more fat than I was 20 years ago. For 25 days a month, my boobs feel about as big as swollen as they used to for the 1-2 days a month before starting my period. And for the 1-2 days before my period, they feel super big and swollen, pregnancy style. Clearly hormonal.
Yes. I hate it. I used to have nice smallish perky breasts and now they are large and in the way plus saggy. No it's not from weight. It's from the breasts growing.