The gas is not uncommon as the gravid uterus (pregnant uterus) will take up much of the abdomen and compress the colon. Stress induced gas is also common in these pregnant dogs.
The inability to get comfortable may be a sign that she is progressing to labor. More importantly, you should pay attention to how many days it has been post breeding. Normal gestation is 62 days so when it gets to 58-59 days you should be getting close. You can also take rectal temperatures and watch for the temp drop that happens ~ 24 hours prior to labor. Normal temp is 100-102. The temp will drop to 97-99 ~ 24 hours prior to labor. You'll also see nesting behavior, panting and anxiety in this time period.
I hope that helps, let me know if you have any other questions.
One other question, is short breaths common also?