Not human pregnancy related

My dog was in heat about 2 months ago... I didnt think she had mated with any male dog but she has gained weight and just today her nipples leaked a white fluid.. im assuming milk.. she is small she is maltese yorkie mix. She isnt pregnant looking but since she is small she would probably only carry one or two pups is it possible she is pregant and just not very huge? I have no experience with this... thanks