Dealing with social anxiety?

i have social anxiety and possable the disorder but ive never been diagnosed,at school i never talk to people,i feel like my mind goes blank,and if i do have something to say i cant!,yesterday we went to my uncles house and seen family,i was unable to speak to anyone there so i watched my sisters swim in the pool so i didn't haft to be around them,ive had alot of depression and my mom just doesn't belive me that something is wrong,what should i do??