Social Anxiety

I've had a hard time talking to people for almost as long as I can remember. Im 17 and I've made zero new friends since this school year has started. It honestly makes me very scared for my future. At first, my inability to speak to others seamed to stem from severe social anxiety. Lately, though, I find that the anxiety aspect has almost completely dissipated and I find, rather, that I don't know how to speak with people. The flow of conversation, although natural to others, seems almost impossible for me to engage in. I never know what to say next, how I should react, hell, I don't even know what facial expression to make. When I voice these concerns to other friends who had previously shared that, they too, struggle with social anxiety, I find that I'm completely alone in my struggle. They say things such as "How are you going to have a future??" or insinuate that I'm  "Just overthinking." I've come to find that their idea of social anxiety and my idea of social anxiety are completely different. It's honestly really difficult being this way. Nobody around me seems to understand. I've come to realise that the difference between their social anxiety and mine is that theirs affects them on occasion while mine affects every aspect of my life. I can't socialize the way a teenager my age should, I take zeros and skip class instead of just pushing through and presenting, I even avoid certain places. My social anxiety is life debilitating. I truly envy them, and their social anxiety. The type where they cant ask for an extra ketchup but they can make friends their age. I'd do anything to get rid of this part of myself.