Constipation/diahorrea/vomiting

Hello!

Have any of you guys had experience of your child being constipated, then suffering with diarrhoea and vomiting then being constipated again? My little one is only 3 months old and he's on infant gaviscon and he's been constipated since being on it, we've tried home remedies like cooled boiled water and fruit juice as advised by the GP and none of those worked. And now he's vomiting alot alongside with diahorrea he's irritable and isn't interested in his food. Just wondered if anyone had any experience/advice?