I strained my hamstring and had to stop running and now I'm getting muscle spasms in my lower back?

Possible. I see lots of low back issues and many are linked to tight hams. Home heat stretching and massage. See a good massage person who will unlock you entire back, gluts, hams and calves. Add in magnesium, epsoms soaking. I love acupuncture and myofasical release w Lidocaine trigger point needling.