If she was only on heat two weeks ago it is unlikely she would know herself if she was pregnant, let alone you or the vet.
Signs such as enlarged nipples, broadening waistline etc. don't usually start to show until at least three or four weeks in. Neither would a phantom pregnancy usually be noticed so early, usually at the same time as she would have her babies if she were pregnant.
Word of advice - if you have a female dog on heat, do not let her play with a male dog who is entire.
I suggest taking her to the vet, just to check she has not got an infection.