I have lower back pain and a sinus infection. are the two related at all?

Sprain/strain: It is unlikely that your sinus infection and the low back pain are connected...except indirectly that if you feel bad/sick because of the infection, your tolerance for dealing with the low back pain will be diminished. Your low back pain can be a lumbar facet issue, a discogenic pain or simply a strain/sprain. You could also have a kidney stone or stone in one of your ureters. See your doctor.