Answer: Hi,
Many women have unevenly sized breasts and during lactation it is common for one breast to produce more (or less milk) than the other. If you weaned 5 months ago and your breasts are no longer producing milk, it is fair to say they have probably returned to the size they are likely to be until you are either pregnant again or, lactating again.
Some women continue to produce milk for months after they wean and although it is not a significant amount, it does mean the breast tissue and physiology of the breast is different to when it is in completely non-lactating state.
If your baby fed more from the side you are bigger on, it makes sense that this side may still be slightly larger. Perhaps you were always larger on that side but haven’t noticed it until now?
It would be worth checking your breasts, just to make sure there are no lumps or obvious (other) changes which are noticeable to you. A check with your GP would be a good idea as well,
Cheers
Jane