Hi there. Thanks for the question. Let me see if I can help
Could he have eaten something he shouldnt have? Gotten in the trash? Part of toy or sock? Soemthing outside?
Is he able to keep water down?
You may want to check his rectal temp. If he has a fever (temp > 39 C), then he is quite sick and needs to get to a vet
Otherwise.....you can continue to try the bland diet you have been doing and give him some Pepcid AC (famotidine) to try to settle his stomach.
The dose for famotidine depends on the size of the dog. If he is 10-15 lbs he can have 5 mg up to 2x/day. If 16-25 lbs he can have 10 mg up to 2x/day. If he is over 25 lbs he can have 20 mg.
If he can not keep water down or continues to vomit despite trying this treatment, he needs to get to a vet in the next 24 hours.
Good luck. Let me know if you have any other questions