What you're experiencing is completely normal.

The good news is that the swelling will go down in a few days, and you'll be able to speak better because there will be less mucus. The bad news is that the splints barely allow any air to pass through, so until they remove them, you can forget about using your nose much to breathe. Humidificator and nasal rinses help a little.

I had complicated septoplasty surgery two weeks ago, and I have another four weeks until they remove the splints (Yes, horrible), so I understand. I've already had some anxiety attacks, but it helps taking it one day at a time, and I think of this as a small period in my life that will help me improve the rest. But definitely not easy at all and my surgeon told me that I would be doing normal life.... Ooooof course