What Causes Back Pain During A Menstrual Period?

hi, I have been in touch with my doctor for my lower back pain for last couple months. Last week I figures the back pain is worst before my period. My doctor suggested it be period cramp. For the past two days I am experiencing strange tangy taste in my mouth with increase saliva. I just went to see my doctor two days ago, should I go for the changes in symptoms. What could be the possible reason?