I think you are being a GREAT Momma! First, it is great that you had the foresight to save the vomit and poo - I always write on the plastic bag what time the specimens were from as well; saving these can be very helpful for your vet. Second, it is not uncommon for dogs/puppies to have upsets. But, for puppies (vs. dogs) - it can be more significant - so while it may be nothing - it is always a great idea to bring your baby to the vet, if you can.
What did the vet say about eating the dandelion? Has he eaten anything now? If it were me, I'd probably go ahead and bring him in, if I could.
