The first thing I would do is be sure the thermometer is calibrated correctly. I use a new thermometer for each pregnancy. I would be sure the thermometer is inserted into the rectum the proper depth which is approximately an inch. Puppies are able to survive after 59 days but pups born earlier have a hard time surviving. If her temperature is below 99F with a new thermometer or the old one has been verified, I would call your vet and see about having an exam done and discuss what options you have at this point. It is best to get as close to the due date as possible.
I am going to give you more information on labor as well. There are three stages to labor. During the first stage the cervix dilates and contractions begin. Your female will be uncomfortable, restless, pace and pant. This lasts 6-18 hours. During the second part of labor, your female's contractions begin in ernest. Her water breaks and puppies are delivered usually after 10-30 minutes of pushing. All puppies are born during this stage. The third stage of labor is after all pups have been delivered and is when a dog still has small contractions to expell fluids and/or placentas from the uterus.
You can read more about this here:
A dog’s gestational period (pregnancy) is approximately 63 days from breeding. You can read about how temperature can be used to tell when labor will start:
You may also notice her breasts swelling during this last week of pregnancy and some milk leakage. Dogs will usually become restless and increase their digging and nesting behavior during the last week. You will notice an increase in her panting as well as a mucous discharge. You may also notice some abdominal contractions or rippling as her time grows closer. Do not be surprised if your dog is very restless and vomits as few times during this last week.
Once your dog's temperature has dropped, please do not leave her alone in case of complications. As she enters actual labor you should be able to see her contractions and most dogs will begin looking at their hindquarters. An increase of licking of the genitals is normal before and during labor. Be sure and have an emergency Vet’s phone number readily available just in case of an emergency during the birthing of the puppies.
Here is an excellent site about whelping.
Some other signs that my dogs always seem to exhibit are lack of appetite, frequent urination and frequent small, runny bowel movements in the day before labor starts. Frequently my dogs will start looking at their rears when the first real contractions start.
I hope you find this information helpful.