[Everglow.]

As somebody who is naturally bigger up top - it can definitely be very normal to have larger breasts. As other people have said, your size can vary with weight loss or gain as well as hormones, and that's all very normal.

As with anything you're concerned about though, talking to a doctor can always be useful, even if it just puts your mind to rest. It may be worthwhile calling up and getting yourself checked over. If it is nothing to worry about then that's peace of mind, but otherwise it can help them to pick up on things they're concerned about and help you.
They can also help you to keep an eye on the impact of having larger breasts on the rest of your body.
For me, I always wear supportive sports bras, rather than bras with an underwire. Firstly they're just much more comfortable as the weight doesn't leave horrible underwire marks on me, but they also help to keep my back from hurting, and keep me comfortable throughout the day. This might be a useful thing to look into if you're having issues with bra sizes and support, as well as general comfort.