I don't think i am allergic to fish, but when consuming fish oil with 1000mg omega-3, i have itchiness mostly on foot. what's wrong?

Coincidence: It's either coincidence or you're allergic. Not all fish contain 1000 mg of omega 3. Omega 3 capsules may contain inert ingredients not found in fish. They're not identical.

Unusual: This would be an unusual allergic response. I would stop the fish oil and if there is no foot itchiness for a week or two, i would resume the fish oil and if the foot symptoms return, this would strongly suggest some sort of intolerance or allergy to the fish oil.