Oh wow, those are the headaches everybody hates ... sorry to hear about your troubles, Emma!
Here are a few things that come to my mind — I've had my share of provisioning errors, too, in the past.
First step: on your Mac, try to compile a simple test-app with Xcode. When you start Xcode, you'll be able to use a default template for that. If that works, you can then try to use the same provisioning profile in the Xcode project that you're using in your actual game. If that does *not* work, perhaps you get at least some error output that helps you in some way.
Furthermore, have you checked if your developer certificate maybe expired? That's what you created in developer.apple.com - Account - Certificates - Development. You said your project stopped working suddenly; an expired certificate would explain that.
On the mac, you might have to install your development certificate in the program "Keychain Access". You can also open that up and check which certificates are installed, if you run into a problem there.
In any case, testing this with Xcode is probably the best way to find out more; it should print better error messages, and you'll be able to google any problems you get there.
I'm crossing my fingers for you! Good luck!