At some point you will notice a whitish discharge.. this will go on throughout pregnancy.. and start from about 3,4 weeks (although you may not notice as most dogs will just lick it up)
But if you see it thats a sure sign of pregnancy

most of the time you cant physically see a change in body shape until about 5-6 weeks.. sometimes later



obviously scans from about 3,4 weeks are a sure sign, but in my opinion its unnessasary stress and money lol