Omega 3 supplement?

I took Jax to the ER yesterday because he had been limping ALL day. The doctor said nothing was wrong with him (I will follow up with his regular vet today). But she did notice his ears were a bit pink and he kept going at his paw pads which is most likely due to allergies. I now have to try and figure out what he is allergic to (food or environmental). I am guessing it's food because I had just changed his food last week to Blue Buffalo and he didn't seem to like it so I got a couple samples of Fromm (Pork & Peas and Beef Frittata) and he seemed to really like both of them. I have no idea if he could be allergic to the Blue Buffalo or Fromm. The doctor also told me to supplement his food with omega 3 fatty acids. Does anyone do this? What do you use and how much/often?

We don't give extra Omega-3 to our bullies. The FROMM we feed them, Pork & Peas has Omega 3 & 6, plus the only supplement we give is HardyPet Complete which has Omega 3, 6, and 9.