I shake all the time, could it be serious ?

From a very young age, i have always had "the shakes". When i was 10-ish i noticed that i shook after doing any kind of sporting activities, but stop after an hour or so of resting, The shaking mainly affected my legs. Back then i didn't think much of it and i ignored it. With time it gradually progressed to other parts of my body and the shaking was noticeably jerky. At 16 i confronted my doctor about it and he sorta dismissed it as a fine tremor, i am 17 now and i have jus noticed that the shaking is no longer triggered by sport alone but by normal day-to-day movements. I'm clean i.e. no drugs and drink and i'm very active and im not overweight. Though i exercise etc, i feel a rather constant sensation of weakness in my joints and have noticed that "normal" things now take more effort. Fluent movements are a thing of the past, i'll try and elaborate: Say i wanted to stretch my hand out, the movement feels like a progression of jerks. any ideas on what it could be? cheers in advance