Aloha! You're speaking to Dr. Michael Salkin
I'm sorry that your question wasn't answered in a timely manner and I regret that I'm not allowed to correspond with customers outside of this venue.
Panting and vocalizing when approached or touched are pathognomonic (specifically indicative) of pain. That pain is likely to be present in a 4 year old Pug's back and is often due to degenerative disk disease - a "slipped disk". Supporting evidence of a disk includes reluctance to jump up or down or navigate steps, trembling/shaking (pain responses), a change in posture - a "hunch" in her back or holding her neck stiffly and head low to the ground, and a normally social dog becoming aloof or, conversely, a normally aloof dog becoming "clingy".
Princess's vet will need to perform a thorough physical exam paying particular attention to Princess's spine. Areas of hyperpathia (increased sensitivity) upon palpating (feeling) her back would be suggestive of a disk. Conservative therapy would then involve the use of a nonsteroidal antiinflammatory drug such as carprofen or meloxicam, a skeletal muscle
relaxant such as diazepam or methocarbamol, and an opiate analgesic such as tramadol. Princess needs to be kept as quiet as possible at this time. Any evidence of paresis (weakness) or paralysis
in a limb should prompt immediate attention from a vet.
Please respond with further questions or concerns if you wish.