I am wondering if you just may be allergic to the type of fish used in your fish oils. Typical fish oils use sardines, mackeral or anchovies. I know certain seafoods like crustaceans make me break out in a rash after consuming too much. This may be the same issue for you. I am just guessing here of course. Maybe you can take a look at what types of fish are used in your fish oil. Maybe try cod liver oil instead as an alternative? Or you can even try Algal DHA. I have heard Matt Lalonde and Chris Kresser recommend algal DHA n3 to be perhaps superior than your typical fish oil.
If none of that works the best alternative is to always limit n6 consumption and try to eat good sources of n3 rich fish a few times a week. I think that is far superior to taking any supplement anyways. Hopefully you figure out what is going on and you get better.
"If man made it, don't eat it" - Jack Lallane
People say I am on a "crazy" diet. What is so crazy about eating veggies, fruits, seafood and organ meats? Just because I don't eat whole wheat and processed food doesn't make my diet "crazy". Maybe everyone else with a SAD are the "crazy" ones for putting that junk in their system.