Unusual shipping help

Hi,

I have an open-cart site, with various products in categories etc

Here is my scenario :

Product Group A - £14.40 for 10kg then 24p per extra kg. (weight based)
Product Group B - 1-3 @ £1.50, 4-6 @ 2.00 etc (quantity)
Product Group C - Next Day £8 for 20kg then 24 per extra kg (weight based)
Product Group C - Before 12 £12 for 20kg then 24p per extra kg. (weight based)

I need it to combine the postage for the whole order, from what I can find its one or the other.

Thanks

Adam

Anyone help me with this ?