my bitch can out of season about 3 weeks ago, i have noticed today that her nipples have became big, she was kept away from my dog when we were not there and when we were we kept a very close eye on them. what do you think this could be? i dont want my bitch to have puppys yet as this was her first heat.

If you're sure she was not mated accidentally, then it's probably a phantom pregnancy. Don't fuss with the nipples just leave well alone and the symptoms will probably clear up without intervention. If things look severe, then the vet can give her something to sort it out.
Dawn R.