Going bald at 15?

Hey, Im 15 and i think im going bald. This all started when one day one of my friends at schools aid. "It looks like your going bald". So i went home and looked in the mirror. I noticed my hair is thinning at the back of my head. Now i havent noticed any hair in the brush or in the drain after i shower. But it IS thinning. Now there is no male pattern baldness running in my family. So i dont know what is causeing this. Ive included a picture. now, Im overweight (ill admit it) and i dont excersice nearly enough. I not stressed (i dont think) about anything in perticular. Im just really worried about my social life at school. Do you know if this is male pattern baldness? or if its stress/Thyroid? And also do you think it will grow back?

[Caryopteris]

Nice head of hair there, actually.  I see the area that might be thinning. Maybe you are eating too much sugar and you are getting yeasty scalp buildup (dandruff).  Try Nizoral shampoo.  You could alternate with Wella Regulate shampoo (order on line).  Nizoral will cause minor increased fallout for the first time or two you use it, but it is slightly anti-androgen and will also control any yeasty buildup, so for those two reasons it can cause hair to regrow.  Eat a low-sugar diet - NO SODA.  Do not smoke as it reduces all-important blood circulation.  Guess what increases blood circulation?  Exercise.  Do it.  

[Caryopteris]

Nice head of hair there, actually.  I see the area that might be thinning. Maybe you are eating too much sugar and you are getting yeasty scalp buildup (dandruff).  Try Nizoral shampoo.  You could alternate with Wella Regulate shampoo (order on line).  Nizoral will cause minor increased fallout for the first time or two you use it, but it is slightly anti-androgen and will also control any yeasty buildup, so for those two reasons it can cause hair to regrow.  Eat a low-sugar diet - NO SODA.  Do not smoke as it reduces all-important blood circulation.  Guess what increases blood circulation?  Exercise.  Do it.