Is my dog pregnant how can I tell for sure

I took her to a vet because I thought she was pregnant 3 weeks ago he says she's not but yet her stomach is becoming very extent extended she is been throwing up she's not eating as much she's sleeping more she goes around the house like hiding little treats in that like she bearing them it's like she's trying to make a bed or something she's 16 months old I took some pictures of her stomach and not so if there's a vet out there who can talk to me I can even send them these pictures and let them see what they think her nipples are a little bit pink so I don't know I'm worried that if she is maybe the pups are dead inside and that's why he didn't think she was pregnant I don't know the first dog I've ever owned

Hello!  I'm sooooo glad you've checked this.  Please contact your vet. You're right that it's possible to get pregnancy diagnosis wrong in a dog, even if ultrasound is used (we are all human).  However this is not the most likely possibility here. Vomiting is not usually a sign of pregnancy is dogs.  What's more, there are other causes of an extended abdomen and vomiting, including some serious things eg pyometra, GVD, cancer, liver disease, ruptured womb, heart failure etc. There is a chance that your girl is seriously ill - please call the vets, explain the signs and ask for an emergency appointment ASAP today so that these things can be rule out. Whatever's causing it, vomiting dogs may need fluids. Please will you let us know how you get on?

In short, please contact your vet and explain the signs and ask to be assessed for an emergency appointment.  I will be thinking of you both so please let me know how you get on.