could i be selective mute or do i have social anxiety?

all my life i have been known as “quite” or “shy”, most teachers would point this out to my parents, and my parents reaction would be she isnt at home. i remember in primary school i was quite towards teachers and other class mates i didnt know very well, however i was able to be myself with my group of friends. in secondary school i remember not being able to speak up in the group of friends i would hangout with and so it became a normal thing for me to not speak at all during the time id hangout with my friends, however i would respond when spoken to or when alone with one or two friends i was more close to but still was never able to be myself with them like i would be at home.
now coming to university and being moved out of my home, there are situations where with my flatmates my mind goes blank and I'm unable to have a normal conversation. when I'm at university, with the friends I made or when having to do group work I can speak up but sometimes I do stay quiet. also throughout school and now I have never been able to put my hand up and ask questions or join in with the class, I always thought it was because of anxiety stopping me but I have realised it's my brain being blank im unable to form a question or thought sometimes.
i have never spoken about this to anyone, however recently being at university where there is more social situations ive been in i have realised something is wrong. i have spoken to a wellbeing specialist at university who believes it sounds like i have social anxiety and i should speak to my gp, however i have not done this yet, mostly because i dont know how to express whats really wrong or i wont be taken seriously as its just something that has become so normal to me as i have been like this my whole life.
sorry this is long, i hope i have explained my problem well enough because to me it sounds very confusing.