Behavior after Breeding

Question
My Yorkie is 4 yrs old and this is the first attempt in breeding her.  Because I work long days, and her heat cycle came during the work week, I am not sure the two of them actually tied as when I was with them I did not see them connect and tie.  However, prior to leaving them alone she was showing all the signs, backing up into him, ears straight up and actually trying to mount him. Likewise he mounted and tried only to repeat the process a couple of times, then it was time for me to go.  The behavior all stopped 2 days after being alone.  They now have no interest in each other, and have had a few growling matches, even though clearly shes still in heat.  In all the research I've done, I have yet to find an explanation as to why, and if this possibly means the tie already occurred.  Thanks for your expertise, can't wait to hear what you think.  

Answer
there is a really good chance that they tied multiple times while you were gone at work but no for sure way to know yet. some dogs want privacy so they will wait until everyone leaves to do their business. a female will only accept a male while she is ready and fertile. the amount of days and how many times varies from female to female. i dont know anything you can do to find out if they tied but make sure  they are kept together for the next week. after 25 days after the day you saw her backing up to him a vet could palpatate to feel pups or at 28 days they can ultrasound to detect puppy heartbeats. i really hope this helps and feel free to ask any other questions you may have.