I just purchased IWD EE and thought I'd load it up for a few minutes of play but it isn't in my library.

Payment definitely went through.

Now I'm looking at my recent purchases and I'm not sure that my September DLC purchases for NWN are in my inventory, either.

How's this possible, and can I please get someone to fix it?

Already did a
https://www.gog.com/account/refresh ?

You got the email receipts of your purchases, right? And it is the same email address that you use for this account of yours, right? (Just checking as there have been some cases in the past where person made a purchase on another GOG account and then wondered why he doesn't see the games on the account where he didn't buy them).

Contact GOG support, they should be able to sort it out.

Funny, i just purchased Icewind Dale as well.

In that case, i would wait. Boot up your computer next day and check whether it's there or not.

The September ones might be worrying, though