If I want to eat candy or take supplements such as omega 3 capsules, do I have to be certain that the gelatin they are made from is not of haram animal extract? As in most of the candys and supplementary capsules found in my country do not specify what gelatin they are made from, usually it just says gelatin on the back. Sometimes they may specify but alot of the times it just says gelatin. Am I allowed to eat such product that do not specify where the gelatin is from according to Sistani?

We have two issues here:
1- The issue of gelatin: If you know that it is animal gelatin, it is not permissible to eat it. But if it is possible that it is vegetarian, then it is permissible to eat it, and it is not necessary to search and investigate.
2- The issue of Omega 3: It is not permissible for you to consume the substance unless you are certain that it was taken from fish with scales. If you do not know, then it is not permissible to consume it.