Anna, I'm so sorry you're having a flare.
While I understand your rheumy telling you to increase your Omega 3 fat intake, I can't understand why they would tell you to increase your Omega 6. Omega 3's decrease inflammation, while Omega 6's increase it.
While we do need Omega 6's as part of our diet, most people get way too much of them as it is. Also, eating sushi once a week won't help much as far as increasing your Omega 3's, but it's a start. You might want to consider taking supplemental fish oil (buy a good brand) or eating wild-caught salmon at least twice a week.
I'm not trying to tell you what to do, I'm just trying to help. I hope your flare doesn't last long and that you're feeling better soon.