I lost everything that I have purchased

So I normally play on the PlayStation 4 and I try to sign into my girlfriends Nintendo switch and after I signed back on my PlayStation for all of my purchases disappeared. All of the maps and all of my skins that I have put money into are gone. It says I have to purchase them again but I am not putting more money into something I have already paid for. Please fix this I have been looking up videos and there is nothing to help.