Just over 6 weeks pregnant and my breast are both equally sore, I've always had one breast slightly larger than the other like most people but now the larger breast has grown at least a cup an half size bigger! Will my other one catch up? And if not will they go back to normal once I give birth? It wouldn't really bother me if it was just temporarily for the 9months,

Most likely you will see some increase/change in both breasts as the pregnancy progresses. One may remain a bit ahead of the other, which is common. Some women notice a change once again if they are breastfeeding, some will find their breasts become similar to before pregnancy, some find they are different. Whether there will be a noticeable difference is uncertain as everyone is individual.