If they gave an anit bacteiral suspension it may be the pup has coccidia which you can read about here
http://www.marvistavet.com/html/body_coccidia.html
or giardia
http://www.marvistavet.com/html/giardia.html
But with the dog vomiting blood I'd see your vet again as this can be due to a viral infection such as parvo
http://www.marvistavet.com/html/canine_parvovirus.html
which they can test for or a problem with a swallowed non food item etc.
Hope this helps you!
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics