How does balding really progress? Really frustrated.

[pick]

I'm a 21 year old guy. I'm pretty sure I'll go bald in the future due to genetics.

(Also, I've been depressed and stressed for the past 2 years due to a particular reason. I'm working to achieve something in life which is really hard to get for me at this age, but I have to do it. The very prospect of it remotely not happening makes me really worried and depressed.)

I've noticed that my hair *density* has become noticeably low.
*But* I don't see any hairfall (on the bed, while bathing, etc. hardly 5-6 fall off.)

But, when I oil my hair during a massage, I can see a lot of my scalp.
My hair is getting really thin. If I randomly lift up some hair I can see some scalp.

My hairline is still good (no change).

Why is my hair density going so low when I don't see any hair fall? Am I balding?

What should I do?