There is a one time opportuntity for PS3 Destiny players to migrate their characters to the PS4 platform. This happens when you log into a PS4 using the same PSN account you use on the PS3 and then start Destiny.
Based off your post it sounds like you already logged into your PSN account on a PS4 and opted to start a new character in Destiny instead of migrating your PS3 characters. Or you started Destiny progress on a PS4, then went back to PS3 and started progress there and continued to play there. Unfortunately since you have Destiny progress with that PSN account on PS4 the option to migrate PS3 game progress is no longer available and there is no way to undo or reset that option. Once done it is irrevocable.
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Okay, thank you for helping me but i'm kinda sad now knowing I can't get it back :/
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You are not missing out on much. Only your characters race, gender and face settings along with certain emblems earned during the last D1 event transfered over. The main in game change you miss are just a quick recap of dates you completed certain activities and small dialogue changes. No items, armour or weapons transfered over to D2.