Dan,
The Browse Catalog sequence diagram shows one unique sequence of actions. In this case, it shows how the user browses the categories, chooses and a product and adds it to the shopping cart. Therefore, I can't really follow what you are saying:
However, he only shows it getting created one time, rather than each time the customer creates an action.
In addition, loops and whiles tend to make the sequence diagrams very complex. Here is what Martin Fowler says about them:
A common issue with sequence diagrams is how to show looping and conditional behavior. The first thing to point out is that this isn't what sequence diagrams are good at. If you want to show control structures like this, you are better off with an activity diagram or indeed with code itself. Treat sequence diagrams as a visualization of how objects interact rather than a as a way of modeling control logic.
That's said, here's the notation to use. Both loops and conditionals use interaction frames, ....
-- Dan