I am a non vegetarian, but whenever I eat fish now, my stomach hurts. What could be the reason for it and remedy thereof?

Fish is a common allergy trigger. If this happens every time you eat fish, then the best option is to not eat fish.

To answer your question, the remedy is... dont eat any kind of fish.

Tick

But I used to have till about a couple of months ago

Specifically what kind of fish do you eat that causes the problems?

Any kind of fish has started to cause pain. Usually I have fish for dinner, it starts to pain within a couple of hours but by the next morning there's no pain!

It could be a reaction during the digestive stage, it depends on how long the pain lasts to tell the problem

Till I sleep it pains and in morning its fine

Stop eating fish