Doubling the quantity in my cart.

When Adding a product to the cart, it is doubling the quantity - so if i add one it lists 2 when i get to review the cart and if i change the quantity to 3 it will change this to 6.Do you have any idea what could be causing this behaviour. Previously I have limited the quantity allowed to be 1 but now i need to be able to sell multiple quantities.

Also when selecting the refresh button on the cart it will then take me to the next step instead of just updating the figure on screen.

Thanks in advance