3 month old Bulldog in pain

Question
Lucy, a three month old bulldog was trying to sit up to sleep today.  She saw a vet who does not know what is wrong with her! Has pain over the left side and he gave her painpills.  Am worried that they may just mask a more serious problem? Any thoughts?

Answer
My first thought would be panosteitis but she's quite young for that. How long has she had this pain? Is it worse in the morning or at night or the same all the time. Does it seem to be in her joints or in her body? Is it along her spine? Does she have weakness when she walks?