Right side of theme shrunk on posts.

This problem only happens on the mobile version. Tablets seem to work fine but mobile phones suffer from this problem.

My website has been working just fine up until recently and has just randomly decided to display this problem. I’ve been trying to find a forum on this problem but no joy as of yet.

The homepage works fine, the problem only arises when you click on a post. The right hand side of the page on any post seems to be cut off/shrunk and the dropdown menu is affected too. Also just recently noticed the same problem on the contact page but very minimal.

Can anyone help? Here’s the link to my site https://www.stancedup.com