I have severe to mild pain in between my shoulder blades and my lower tailbone, what causes it and what can I do to fix it?

Most likely not rela (carisoprodol) -ted, but see your PCP 4 eval & referrals as needed. .
Muscles . it is uncertain. This could be muscle, it could be part of a medical issue, or some other diagnoses. You need to see your physician, possibly get imaging, and maybe physical therapy.