Could you please help me with salmon oil for shih tzu 3 months 2.3kg puppy? Which one should I purchase from the market?

My puppy had his last dose of rabies injection yesterday. He is having diarrhea since last night and vomited the curd rice breakfast I gave him in morning. What shall I do doctor. The doctor at the hospital had told he will have liquid potty but I think this is making him weak