Hey i am 15 and i have an anxiety prob whevr i am not doin somthn i get realy anxious can u hel ho do i ridit

Whenever i am not doing something i get really anxious. i cant really explain how i feel but it sux. I only usually get it in the afternoons. if i watch tv or do something that realxes me it goes away. However it is very hard to rid and i don know what to do. plz plz plz help me.