The website <docsouth.unc.edu> "Documenting the American South" presents a list of perhaps 200 diaries and journals compiled during the War Between the States. Most are not Shiloh related, but some make mention of Fort Donelson and Shiloh (Mary Chesnut, for example.) Just about every diary has a link allowing online viewing:
https://docsouth.unc.edu/fpn/texts.html Documenting the American South.