Confused!

Question
Hi, my name is Nick. I have a Jack Russell, Gracie, I am just curious about a couple of things. First off how long does their heat period last? This is her first heat. She is eating Iams puppy formula. Now another thing is that I am afraid that she may be pregnant. Is there a way that I can tell without going to a vet? Her mood has changed from being hyperactive to calm, she is gaining weight and her nipples are enlarging just a bit. Her vagina is black to purple in color and she is humping my leg every once in a while. What is this about? Please help.

                           Thanks
                               Nick

Answer
Hello the heat normaly lasts 2 weeks, Leg humping is a sign of wanting to mate or shes trying to domnate you...I have noticed my dogs mount and hump each other even thou all are Spayed/Neutered this is for domance ranking. Four weeks after you think she got pregnant you should viasbly be able to tell her tummy is getting rounder until then you could get an ultrasound via a vet but I wouldnt elt anyone prob my dogs tummy when shes pregnant or might be pregnant it could cause a miscarrage early on so best wait and see yourself. Nipples get big when teh dog comes into heat they should go down after the cycle is finished if not shes likely pregnant. the nipples will be bigger yet two weeks before shes due to have her puppies. Pregnancy lasts 60 some odd days.