receding hair line can be early sign of genetic male pattern hair loss. You may want to see a hair loss specialist and use hair loss medical regiment under supervision.
You appear to be developing a receding hairline which is caused by genetic hair loss. See a hair specialist who understands that if you are under 25, you should be started on finpecia daily for one year and see what happens.
There's more to diagnosing hair loss that simply a photo. You're right - the most likely diagnosis by far is male pattern balding. But your story is what confirms it. If you lost your hair in a period of one week - it's not male pattern balding. It's a combination of the patient's story of their hair loss PLUS what the pattern looks like that helps solidify the diagnosis.
Overall, the most likely diagnosis is male pattern hair loss