The weather would not have her acting lethargic. I would check her gums and make sure they are pink and moist. If they are pale, white, gray or blue she needs immediate help.
I would take her temperature rectally and make sure she does not have a fever. A fever can indicate an infection in the body.
The not eating is another worry it can signify an upset stomach or a blockage of the intestines. If she eats any non food items such as rawhides, bones, greenies, bully stick, toys, etc. then I would worry more of an obstruction.
If she eats any fatty human food such as pork, steak, etc, then pancreatitis can come into play.
If she has gotten into garbage then garbage toxicosis would be cause for concern.
Obstruction (foreign body)
Garbage gut http://www.petplace.com/dogs/garbage-toxicosis-garbage-gut/page1.aspx
nmormal body temperature for a dog is between 100.5 and 102.5. You can use any thermometer, if it is not a digital one then hold it in the rectum about two minutes.
gas x can be given to dogs for excess gas as well can pepto bismol. since you are worried I am going to direct you to a site on how to take the normal vital signs of a dog. This may help you decide if something is not right.
I can direct a vet to you, you have psoted in the dog area not the vet area, is that what you want me to do?