i need help !

ok so im a cna and i have a very demanding job and ive noticed my body being sore and such from all the lifting and sruff like that but for a week now the back of my left shoulder and an uncomfortable feeling like pressure and it gets a pulling feelind and sometimes and if i sit a certain way it hurts it mainly hurts while sitting or when im busy dpinf something and when i reach to touch it with my other arm its tender burns any nurses or doctors who can tell me what ik need to do that wpuld be GREAT!