My Rotti wont come into heat

Question
I have owned a female rotti since she was 3 weeks old. She turned 5 years old last October. She has had three heat her entire life; the first when she was under a year old, the second when she was about 2 years old, and the third when she was about 3 1/2 years old. She is an inside dog, getting the finest of everything. She is my baby and goes everywhere and does almost everything with me. I would like one litter of puppies before she get too old. I have found a lovable perfect tempered male to breed her with. She just won't come into heat. She is on Nutro Natural Choice Lamb and Rice for Large Breed dogs for dry food and she gets 1 can of Nutro lamb and rice wet food every morning. She is on Frontline for fleas and ticks, and Zimectrin for heartworms monthly. She weighs 90-100 lbs. She is in great health. She lives with a spayed female and is often around a fixed male. My question is what can I do to start her heat cycle? What could I do to try to bring her into heat? I have read about a natural supplement from solid gold concept a bitch, but I am unable to find it on the market anymore. I am not out to try and breed my baby to death, I would just like a couple of puppies from her. My parents, parent in laws, and siblings all want a puppy too, so I know they'd have great homes, if I could get  any. I am just discouraged and looking for answers. I would appreciate any advice you could give me. Thank you in advance, Katy and Abbi!  

Answer
Katy,
Take her to a vet that specializes in fertilization.  Or find one somewhere and call and ask for his help.  I don't know where you are so can't recommend one.   Make sure he knows about breeding.  You will find these vets also work with horses and cows.  There are ways to bring a bitch into season, but a vet has the best stuff to use.
nancy