Hi and Welcome
My female came into heat around five months after she birthed her puppies. We just had her spayed. I think you did well to wait until she was almost 2 years old to let her have her first litter. I had mine spayed because we didn't plan to have a litter in the first place and I had heard it is healthier and that they live longer if they are spayed...but I also know that is debateable. We are not breeders and didn't have any reason not to have her spayed. I'm not sure but I don't think it's too healthy to breed them one cycle after another. Our puppies were born on 4/01/05 and Bitsy just came out of heat about two weeks ago....so YES, she could probably be going into heat again from what you described. Maybe someone else here can give you some pointers and I would separate them. Are you a breeder?