Left sided pelvic pain radiating to lower back?

Could be. Many different things, from ovarian/uterine issues to left sided colon issues. It could even be from your left kidney/urinary tract system. It would be very helpful if you could provide more information in regards to the quality of the pain, what makes it better or worse, anything else going healthwise and what may have been going on when it started.
See gynecologist. Knowing that the ovary is located there, see your GYN. While there are many reasons for pain in that area (diverticulitis, for example), the possibility of a ruptured ovarian cyst, or even an ectopic pregnancy exists, so it needs to be checked.