Interesting thread. My omega 3 index was also low, and it was tough to find a supplement that did not cause stomach issues and disgusting smelling burps. In hindsight, I was not breaking fish oil down into usable nutrients due to a lack of pancreatic enzymes needed to break down the fat.
Once I started taking pancreatic enzymes and fish oil supplements I went a bit overboard, which affected my cholesterol. Specifically the DHA component in fish oil can increase LDL cholesterol, whereas the EPA component can slightly decrease LDL. Both EPA and DHA can decrease triglycerides. In one of my experiments, when taking three grams of fish oil per day for four months, my LDL cholesterol increased by 21%, HDL levels increased by 11% and triglycerides decreased by 10%. But, taking three grams of fish oil per day is roughly equivalent to eating one pound (454 grams) of fish per day!!
Genova Diagnostics has a great add-on to their nutritional test for Essential and Metabolic Fatty Acids Markers (RBCs) which details levels of multiple Omega-3,-6,-9, monounsaturated and saturated fats. It was a great way to check how changes in diet and supplements impacted my levels.
There is a prescription version called Vascepa that is EPA only without any of the heavy metals and toxins that you have to be careful with when sourcing fishoil supplements. And I have no disgusting burps or stomach issues with that one, but those issues might have been due to not being able to break down and absorb fishoil.