Gracie,
I always had lower back (and pelvic) discomfort during the start of my period. Also, the last couple years I had a lot of flooding, requiring me to mostly stay home the first few days of my period, for fear of bleeding through everything - truly a pain! I even had to lay towels on the furniture... The doc recommended some testing, and all was normal - just peri!
What helped a lot with the discomfort was to take Advil, recommended by my physician. Supposedly it helps calm the prostaglandins which can cause pelvic spasming. I'd take it at regular intervals (using the recommendations on the box) for the first 2 days of my cycle.
The good news is that I'm now just about 3 years post-menopausal, and yes, we really do stop bleeding one day!

It is HEAVEN not to have periods anymore, and all the highs and lows of one's cycle. No tampons, pads, soiled clothing. I went out and bought all new undies and nighties. AWESOME!
(((BIG HUGS)))
JJ