I'm 17 year old teenage boy who is experiencing hair fall and hair thinning! What do you think is happening to me?

What you are describing can certainly be due to genetic pattern baldness. Although your current family and relatives are not showing signs of hair loss, the genes responsible for androgenic alopecia (i.e. common baldness) can certainly skip generations.If your condition is not due to genetics, it is possible that your hair loss could represent some type of telogen effluvium (i.e. temporary hair loss caused by bodily stress). The stress can be due to events like surgery, or even what people might consider to be psychological. Stressful life occurrences can exert an influence on neurochemicals which may affect the hair follicles.
The best step to take would be to speak to a doctor and get a diagnosis. This will help you understand which course of treatment would be relevant to your situation.

If you are losing hair want to know why, it is best to see a doctor for an examination because as you rightfully point out that looking on the Internet will only give you "theories and intelligent guesses".

No one belittles the loss of hair and how it can affect anyone, especially at a younger age. Our hair changes at some points in our life due to hormonal changes in our body,. This is a natural occurrence and settle down over a period of time. There are many causes that can increase hair shedding if that is the case. A change in the natural growth cycle causing the hair to shed the follicle prematurely, creating the imbalance in the growth to dormant phase. We normally have around 90% of our hair visibly growing. Before any signs of actual thinning it can take a high % for this to become noticeable. It would be prudent to visit a specialist if you are this concerned and maybe have a diagnostics check.

There are multiple causes of hair loss which cannot be treated without proper history and physical examination. Thus, it will be better for you to visit some hair specialist and get a proper treatment from him to solve your problem of hair loss.

Hair Loss can be a traumatic experience especially in one so young. I would advise you visit your Doctor and speak with a Dermatologist to seek a professional opinion from them at this stage.