Depending on version of android on your phone, you might have a cleaning utility built in ... this would help you jettison old apps, free up storage space on both the internal side or the sd card side. Might also help you determine if the SD card is being seen, or has other issues.
If no built-in app, it's easy enough to get one from the play store.
Depending on phone, there might be updates to the phone os that "fixes things". If no updates, then there's bound to be an app for that, to help troubleshoot things.
Hope this helps ...