You say you’ve just noticed that one breast seems “much bigger” than the other. It doesn’t have any additional sensitivity and otherwise looks the same as the other, and you had a normal mammogram earlier this year.
Most women have breasts that are not an exact match in size, but it’s typically a life-long reality, not a change. Breasts becoming larger isn’t normally a concern, since they change as we gain or lose weight, have children, and grow… more mature. Again, what’s “typical” is that both breasts are affected more or less equally by a change.
If one breast is changing, it’s a good idea to have a clinical exam by your healthcare provider. That’s a noninvasive way to assure that everything’s okay.