Random vomiting

Hi all, this is a long one but I appreciate any advice! My son has been sick on and off since last Saturday night, he was unwell in himself on Sunday (legarthic, contact naps, not playing etc) but has been well otherwise since with random episodes of vomiting: Saturday- 5pm and 8pm Sunday- 1am and 6.30pm (Nan was sick also) Monday- 9.30pm Tuesday- 6.30am Wednesday- 6pm Thursday- nothing! (I was sick at 3am and had diarrhoea) Friday- nothing Saturday- 1.30am He’s had a pretty plain diet most of the week and no new foods. Is this a bug? The randomness of times is so confusing In this something more? Should I get him seen? Is it gut motility? Is it an allergy? If you’ve got this far- thank you! Any advice appreciated.