Hi tremors can be due do excessive strain to muscles due to work out...other causes can be hyperthyroidism,drug induced,essential tremors,cerebellar problem etc...consult neurologist they will the cause and treat accordingly

First of all you have not mentioned from how you have this shivering... and is it through out the day?? or only after going to gym?? It could just that you are exercising or pushing yourself too much beyond your capacity... if it is only after exercising, reduce your workout and observe.. and have some mild caloric food before your workout..