i just started bodybuilding and i am 17 years old but for some reason when I do benchpress or some other exercises my arms starts to shake though also when i do arm wrestle they shake too and i don't think the weight is the problem because if i lower the weight i may stop shaking but after my workout I don't feel anything and if I keep the same weight and I do my sets I feel sore for the next couple of days, so what is going on? thanks on advance