Currently when members post things on my website, they can't see what they posted via their profile. How do I fix this? 

 

Please change the front end to an unmodified Theme, and disable all 3rd-party apps and plugins.

Does the same problem happen?

If not, then the issue is with either your Theme or one of your 3rd-party items.

But if it still happens, please reply here to let us know, with details of what they are seeing on their profile page and where within it.

How do I change the front end ? 

Do you mean how to change the front-end Theme?

If so, go to ACP -> Themes and edit an unmodified stock Theme (create one if necessary with the green "+Create New" button). Once open for editing , enable this setting and then save:

 

Once the page refreshes, use the drop-arrow menu to the right of the Theme you just edited and choose "Set as Members' Theme".

That will set an unmodified Theme for the front end.