Hi - I have noticed that my problem is related to my cycle - so it is something that is hormonal for me. Sebamed is not just for women. It is a bodywash that is closer to the skin's natural pH. When I use regular soap, the fishiness intensifies. The enzyme that is needed to break down the product that causes the fishy smell is made up of Vitamin B2....so for me, taking extra Vitamin B2 helps the enzyme to be made properly. If I were you, I would do a Bowel Cleanse like a colonic or a high dose of magnesium citrate (2 Tbs) to clean out the gut - if you do the mag citrate, do it over the weekend because you will be going to the bathroom for a few days. Drink lots of water during this time as well. Once you are done with cleansing the colon start taking probiotics, eat low choline foods and foods that are whole and natural. Take a multiple vitamin without Choline and take 4 -5 capsules of 100 mg of Vitamin B2 a day until you notice the smell is gone.
Also, try to take note if the smell is constant or only during certain times. Most importantly, try to control stress.