I have been dealing with a shaking sensation when my muscles are under stress/load?

22 y.o. male. No PMHx besides fractures of lower leg and left wrist. Recently I have been dealing with a shaking sensation when my muscles are under stress/load. For instance, when I slowly walk down the stairs or if I were to squat for an extended period of time, the muscles in my legs will become very shaky. Another time I notice it is while laying down, if I were to sit up slightly to grab something, such as my phone, the muscles in my abdomen do the same thing. I have also noticed it when lifting heavier objects. While I know if it were just my legs, I could attribute it to weakness perhaps, but with it seemingly effecting all the muscles in my body, I do not feel as though this would be the cause. I met with my PCP a few times about this, and so far all blood work as been normal with the exception of my Vitamin D level which was low. I have been taking a 50 IU Vitamin D pill 1 time per week for a month now (4 doses) and my symptoms do not seem to be improving. I have also noticed a shake, or almost a tremor in my hands/fingers at times. As I am typing this when I have my wrist/palm on the table and my fingers above the keyboard, I notice a shakiness in my fingers. Im beginning to feel slightly worried that I might be dealing with something a lot more serious than a vitamin deficiency, like a neurological disorder. Any insight or ideas would be greatly appreciated. Thanks in advance.