I just placed an order, has my credit card/PayPal/AmazonPay account been charged already?

When you place an order using credit card as payment, the order amount is automatically reserved on that card.
Note however that a 'reservation' is NOT a 'charge'.
Once your order is shipped, this 'reservation' is converted into the actual charge.
In the event that your order cannot be shipped, like when an item is out of stock, the reservation will remain for 30 days before automatically expiring.
This same principle is also true for Paypal and AmazonPay: the reservation remains until either order shipment or for the maximum 30 days (180 days with AmazonPay).