You need to call around until you find a vet who will work with you and allow you to make payments because you cannot allow your dog to go on like this. From your description she is in considerable pain, and it could be from a back injury or it could be from something like pancreatitis, which can be life threatening if you do not have it treated. Please do not wait any longer. Start calling around NOW.
Janis is right, sounds like you dog needs to see a Vet. This could be a back injury or possible pancreatitis, etc. you need to borrow the money or some Vets will let you apply for credit. People fall on rough times for whatever reason but part of owning a pet is being able to care for it properly. Hope you were able to find out the cause for her discomfort. Please come back to update.
Sorry but is sounds like she may have hurt her back or pulled a
muscle and the ONLY way to help her is GOING TO A VET. IF
you can not afford your regular vet call around,find a different
veterinarian to help her.
IF IT IS A BACK INJURY,many times the sooner they recieve
care and treatment the less likely it could become a permanant
injury...IF SHE IS WHIMPERING SHE IS IN PAIN...
THERE IS NOTHING to do to help her at home she sounds like
she needs professional intervention as soon as possible