What could be the cause of hair loss in a 15-year-old boy?

Hello doctor,

I am a 15-year-old boy, and about two weeks ago, I noticed my hair falling out. Every day, I wake up with two to three hairs on my pillow; on my bed, there are about ten hairs. Every time I run my hand through my hair, about five to seven hair strands fall out. Every time I shake my head or hair, I see about two to three hairs fall out. During the shower, when I apply shampoo on and start rubbing it all around my hair and check my hands, there are about seven hairs on each hand. Sometimes I do not even have to do anything, I could be watching a video, and I see at least one to three hairs on my bed out of nowhere. My hair is about 3.5 to 4 inches long. I have never experienced this problem at all until two weeks ago. My twin brother does not have this problem at all. I have told him to shake his hair, and no hair comes out. Run his hand through his hair, and no hair comes out. He just does not seem to have this problem. No one in my family has had hair loss problems. I used to apply hair products to my hair, like gel and hair spray, but I never had any problem, and I stopped applying those hair products about 1.5 to 2 months ago. But like I said, I recently began to see my hair falling out little by little. I have told my parents about this, but they say I should not worry since it is not a big problem. I know we lose about 100 hairs a day, but come on, really?

I am sure we are not supposed to see hair fall out like that; I am just so sure. I have avoided hair brushes and hair products. And by the way, my hair is straight. I am not taking any medications at the moment. Please help.