Many times when people ask me to do things I feel like I don’t have the power to stop or refuse them

it can take some time to learn how to stand up for yourself, because oh well, it's not that easy... let's start with some simple steps- explore where your difficulty in refusing people when they ask you to do things comes from, reflect on things from your past that might impact your relationship with 'power' in certain situations, understand how this feeling of powerlessness impacts your life, and learn to assert yourself and your needs :)