Small dogs are predisposed to spinal problems. Specifically they have a high incidence of intervertebral disk disease (a slipped disk). When the slipped disk is in the lower back (behind the ribcage) these dogs have problems with their back legs ranging from pain and weakness to loss of coordination to paralysis. When the disk is in the neck area they have severe pain, often walk around with their heads down, are reluctant to eat from low food and water bowl, turn their whole bodies towards you when you call them (rather than turning their heads), and start to "shake out their fur" but then stop because it hurts. Does this sound right?
Try moving your dog's neck to the right and left, and up and down. Does it hurt?
Feel your dog's belly is it tense? dogs with lower back pain tense their abdominal muscles to help splint their back bone.
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If she has no gastrointestinal signs like vomiting and diarrhea, it is likely her back. An antiinflammatory, muscle relaxant and pain medication would probably help. You can get these by visiting your vet. You'll also get a second opinion that way by someone who can actually see your dog. If he/she agrees, I would cage rest her for 2 full weeks (STRICT cage rest). That does 90% of the healing. The medications are only 10%. In fact, the medications shouldn't be given if you can't strictly cage rest.