Is my dog pregnant???? Help.?

Okay, so my dog mated on May 21. I took her to the vet at around 22 days and they took blood from her, it was negative. They told us to come back 10 days later at 32 days and it was negative again. It should now be around day 45 in her pregnancy (if she is pregnant)...she has gained alot of weight, and her nipples are huge. I