The number relates to the size round your chest with no boobs, in the UK is a different number and it is actually the number of inches e.g. 34, 36 etc - so this is my theory - being a mum is hard work and lots of lifting is involved, so you have developed upper chest and back muscles making the 'number' bigger (the number can be different due to carrying more weight there too but sounds like you aren't). Also I think is really difficult to measure yourself accurately so you might find that if you get measured although you get a 14 they get a 12 for example.