I'm having the same issue. I've been taking quite a bit of fish oil, as well as seriously increasing the amount of fish I eat for the last two weeks. I have had insomnia coming on for almost a week, getting increasingly worse until the night before last when I woke at 2 am and couldn't get back to sleep.

Last night I didn't take any and slept like a rock. I did take some in the morning yesterday.

I googled it and apparently some people get insomnia and anxiety with fish oil. I'm going to continue taking a small amount in the morning for a while longer, but my long-term goal is to get the omega 3's from my diet - fish, leafy greens, flax seed, etc. - and decrease the omega 6's I'm consuming.