Have decided to sell some of my baby's clothes and am confused about royal mail postage rates. I have bought a fair few items recently and they have all come with a label on with a random price- anything from about £1.50 to £3.50. All either first or second class. I have been on the royal mail price finder page but all that comes up is £3.20 once you go above large letter for second class. What am I doing wrong please? I want to work out my postage.