Hi Vic! I had the same problem I got 2 degus from a pet shop, which I was informed were both male.. 3 weeks later one gave birth to 4 babies, I took them all to the vets a week later, and was told that the 2 males were in fact both female.. The babies turned out to be 3 girls and 1 little boy.. As they can breed from a young age I put the boy in his own cage, and when he was old enough I had him neutered.. This itself was not easy as he has many problems, which I will not go into detail about, except he had to have mayor surgery and was very sick.. I will explain if you would like to know..
I have not noticed any size difference, the males are supposed to be a bit bigger, maybe because we had him done at such a young age he wont get that big..
If you need more help, I suggest asking a vet, and get them checked out also..
Hope this helps?
Feel free to PM me, if you want to chat..