HI Princess Kirra,
Swelling of the abdomen and mammary glands can be a sign of pregnancy, but to be certain you should take her in for a sonogram to confirm as dogs do go through false pregnancy during the third stage of the heat cycle which will show the same symptoms of a pregnant dog. Another important factor is if the dog is pregnant who the father is. A male dog lthat is larger than she can cause problems during birth as the pup may be too large to pass through and a C section may be needed. I am going to direct you to a site on pregnancy and false pregnancy for futher reading.
That makes it possible as a male can procreate at the age of six months. This is why neutering is recommended before six months of age. IF you actually saw the two tie then it is more likely. Now a problem will lie also if you wish to register the litter with the AKC, as they will not register them if the male is under a year old.