The flash you describe is most likely vitreous traction. You should see a retinal specialist.
Dr. O.
It is unlikely to be vitreous traction as the flash he described has a shape.
I know because I have your problems, the floaters, the flashes with shape, and the trails. I took an MRI, blood scan, and numerous eye tests and have seen many, many doctors, all turned out normal. my neuro opthamologist finally diagnosed the problem as palinopsia and told me to be under observation for the next 5 mths.
Do realise however that those flashes and trails may seem more prominent as you are increasingly vigilant about your vision, and flashes and trails are perfectly normal when they don't last too long.