Dermatologist won't prescribe finasteride. Can I start on my own?

Hello! I'm a 20 years old male with long hair. My hair has been thinning for the past 2 years. Though it is not noticeably bad when I let my hair loose, it's a different story when I tie it up. I have recession on both sides, which many people think is just a mature hairline. I have thinning all over my scalp apart from the sides. I've tried to use saw palmetto to block a little bit of dht. It made my hair more fuller, but hair-fall hasn't stopped. Should I take finasteride?