I'm not really a dog person, but looking around a number of sites it seems that by this stage you should notice the female wanting to eat a lot more, and her nipples should have become enlarged (usually around 2 weeks).
Whether you can actually see signs of puppies seems to depend on the dog and the likely number of pups. The majority of sites mention that you should give the dog a slightly different diet if she is pregnant around the 6 week period, but not much information on what apart from speak to a vet.
Regarding the breeding - did she mate about a week after she became "on heat" as that seems to be the prefered time. From what's described, the discharge should go clear and that's the only time it is likely to work.
Many of the sites also note that it's very much like human pregnancy in that it sometimes takes a few attempts so it's not guaranteed that she's infertile at all.
Best idea might be to take her to a vet and see if there's any likely conditions, assuming she's not showing the signs of pregnancy. Could be that she's just not hit the right time, something like an infection or even that the male dogs weren't exactly working at full form.