
Once again (risking cries saying I'm wrong) why bother!!! If you had a couple of really good matings, plan on a litter and wait. Yes, it's frustrating, but in any case, by about week 7, you'll see puppies moving around. A scan at this point will only confirm a pregnancy, or not. Not that she'll carry to term and as they are not accurate, not how many either. If she goes over by more than a couple of days, then it's time for a vet trip to examine her, and probably x-ray which is far more relevant, and accurate. If you want to do this, that's your decision, but just know we have never bothered.
If you know your bitch well, you may find she's a little more 'careful' of herself from the beginning, and a thickening of the flanks by around the 4th-5th week. And with mine, the vulva rarely went back to 'normal'. But again that doesn't mean she'll carry to term. I had one showing all the signs at 5 - 6 weeks, and then she didn't get bigger. She had one singleton puppy - and probably reabsorbed which is very sad.
Good luck - scanning is your decision.
If she's attracting your male/other bitch, check her anal glands. And do keep an eye on her for any discharge - unfortunately occasionally a bitch can pick up an infection during a mating. Hopefully not. And in this case, maybe a scan might be a good idea, to rule out a pyometra.