Hi welcome to the health care magic According to history you have consumed fish yesterday.. And than your complaints started, hence yes it seems to be food poisoning case means food toxin induced gastroenteritis... Because of lost fluid and electrolyte in stool headache is present. . Maintain hydration with lots of water... Take ORS also for three to four days to replenish lost electrolyte.. Take tablet racecadotril that is antisecretory drug... Probiotic tablet like vizylac taken to replenish lost bacterial Flora... Avoid irritants to stomach like..... -Excess tea, coffee -Smoking -alcohol -meat etc Small meal taken with frequent interval and excess fried food avoided If no improvement than stool examination, CBC etc needs to be done For cold decongestant like benadryl can be Prescribed Take care Consult physician for examination with keeping all this in mind Hope your concern solved