Fish oil is really a food source. You can eat salmon more often, and use flax oil and see how that goes instead if you prefer.

Depending on your dose of fish oil, start with one a day with a meal, and increase say in a month to 2 a day, etc. 3 a day should be enough eventually. But many people do well on less.

If you don't consume omega-3s in food, your whole body will eventually deteriorate. They are essential.
The omega-3 in flax oil is alpha linolenic acid and cannot be made by the body. The omega-3's in fish oil are made if all is going well chemically inside you, from the alpha linolenic acid.
Females convert fairly well from flax to EPA and DHA (which are in fish oil). Males are less efficient in this because they do not carry babies who need high levels to develop the nervous systems during pregnancy.

Essential fats require B6 and magnesium to incorporate into the tissues of the body. Without the support nutrients they will fail.