Nice quick game of point and click. I liked the puzzle section of investigating first to get all the equipment and then reading through the notes. It was a little hard to decipher the instructions, but not impossible. If that's what you were going for then you've succeeded.
For sound the music fits really well. I suggest adding a swish sound when gaining an item. A page turn sound when looking at notes. Praying could use some sound (The classics are a Vocal Ahh, murmuring, or chanting. Though to fit the calmness, maybe just rustling of cloth would work). There's lots of options for the treatment, but I'm sure you've got ideas.
The text could use some line breaks like how a <br> element looks to delineate separate entries and make it easier to tell which text is new. I found myself rereading previous text because I couldn't tell where the new text began due to the scroll not moving to the top of new text.
For the treatment minigame, it would help if the value change text was highlighted somehow. Bolded or italicized or white for good, dark red for bad or something like that. Another minor thing that could improve it would be to add a lerp to the number change on sanity and infection stats as well as the color coding mentioned.
The art fits well. Though the background seems a little stretched horizontally. Take a look at the settings for Expand Mode and Stretch Mode of the TextureRects.
The color for the buttons seem decent, though I think they still need something.
I liked the visible green fog disappearing after curing the diseased. It could probably use a small animation of fading out to transparency.
It would be nice to be able to reread the investigation text after leaving and coming back. Though maybe make the button a different color to show that there's nothing new.
There were only a few bugs. The Pit investigation button can be pressed multiple times and it prints the text again. The Well's investigation button doesn't disable itself.
All in all a good entry. First time I ran out of sanity, but the second time I was able to figure out how to balance the stats and win. Congrats on your first game completed!