This can be a common problem with fish oil. I usually suggest that people take it after their largest meal which is usually dinner. Personally, I have found this to make a huge difference. Also, make sure you keep it refrigerated.
If this still does not work for you I would suggest switching to the capsule form. You can either look for an enteric coated softgel (won’t break down until after it leaves your stomach ensuring no fish burps) or get regular softgels and store them in the freezer. Freezing them is an easy way to make them enteric coated.