What could be wrong with my pomerainian?

I just got a pomerainian from a breeder who has had her for a year. They named her pebbles, so I decided to let her keep that name since she is used to it. Well lately she's been vomiting a lot like hours after she's had her dinner, and when she has a bowel movement the stool is all runny. We've tried giving her over the counter puppy medicine and that didn't do any good she just vomited that up to. What could be wrong with her? Is she sick? Do I need to take her to the vet?