Tolerance change or am i sick?

Ok so lately around where i live in the bronx weve been getting some really good bud ( kush, blueberry dro, diesel) but for some reason i dont get that high anymore....now when my friend got kush he gave me .8 to try out so i rolled up a blunt and got very high, but two weeks before that i was smoking diesel, silver haze and some very good dro and not getting high....im 15 and ive been smoking since i was about 13 now myfriends who have smoked better bud and for longer still get high as hell and i dont does anyone know what the reason im not getting high is? I think its cuz im sick. thanks