Not flashes but flicking lights. 36 weeks?

Could be a migraine. Headache + flickering lights = migraine, for me. Hormones definitely make them happen more for me, so who knows, you're very pregnant, maybe the hormones are doing it. Keep an eye on your BP, even go to the drug store and check it in their machine every few days, if it goes up, or you have more or worse symptoms, go to the doctor ASAP.