Why can I not stick to anything?

I'm 17 years old and over the last 5-6 years I have tried almost every activity/hobby from fishing to skateboarding.
I seem to always be extremely insterested for the first month or so then I totally lose interest, can anybody suggest how to make me stay interested or even suggest interesting or sustainable activities.
i have tried
fishing
gaming
BMXing
Skateboarding
football(soccer)
i have dabbled in most sports

i think i may not be able to sustain these activities maybe to do with my shyness as all hobbies already have a group of people expirianced in it.

Gym is great to socialise and u can do multiple activities in one day. Group classes are great and yoga really makes you thing about whats important in life.
Try horseback riding or rockclimbing!
Dont give up when it gets hard! Push through!
Goodluck