There are several reasons for your tremor, ranging from Parkinson's (for which you, according to incidence statistics, are too young) and cerebellar ataxia (unlikely without other neurological deficits or a previous history of trauma) to benign muscular apraxia. The only way to know would be to perform a physical examination.
You say that your whole body shakes, and that is, in its literal sense, a neurological symptom. However, seeing that you just started working out after a long period without physical activity, the most likely etiology is that you have poor inter- and intramuscular coordination.
Basically, your brain and muscles aren't used to performing those movements smoothly and efficiently. This always happens during the initial phases of training, even for experienced athletes after years of training with a short detraining period, but also when doing a new exercise.
In case your tremor does not subside within the next 5-6 training sessions, or at least improve, then it is likely something else. If it does, then you have nothing to worry about, there is no need to control it, and it will go away on its own once you get more used to performing those movements.