It looks like from the name of your custom theme that you made a few tweaks to the navigation of your site. It's possible your changes are causing the issue - try switching back to the standard theme that you originally modified. If it works good there, you can try remaking your edits again.
We don't provide assistance with custom HTML and CSS changes, unfortunately, so I can't troubleshoot this for you. Maybe one of our Community members can help, though.