Page links only working with S at the end?

Okay I’ve been uploading alot of pages on my site here today and it was going very smoothly, until one page and now every page I create or edit only works if the link ends in an s. For example, I created my “content” page and it was working fine. The permalink WAS modernrevolutions.net/content, however I edited it a little while ago and click update, then click view page and it said

Error 403 – Forbidden

You tried to access a document for which you don’t have privileges.
But when I edit the URL/permalink to have an s at the end to make it “contents” it works. Anyone know how to fix this? Its really annoying