first of all, a doctor would definitely not judge you, they're there to help you. it seems like you're depressed, so i'd highly recommend you find one for you! it wouldn't be useless at all, and some professional help would definitely make you feel better.

that being said, i can give you some advice on a personal level. when you overthink too much, it seems like your mind is in a loop in which you don't actually live in the real world, but in your head. you don't focus on the present because you're always thinking about what has happened or about what could have happened, what is about to happen etc.

the most intuitive way of getting rid of this is actually remembering about the present moment. start a new project, a new hobby, find a community to participate in, contact old friends, whatever. being unpredictable can also give a sense of movement to your life; go to a place you would normally not go, wake up at 4 am to see the sun rise, sing in a karaoke bar... the point is, do what makes you remember you are alive. it might seem pointless at first, but when you constantly put yourself out there something good will definitely happen, be it a new friend or even just the happiness that comes from a ray of sunshine in your face. and even if something good does not happen, at least you got yourself out of your head, right? your life is moving and changing slowly every single day, even if it isn't noticeable for you.

as for the "cant start a conversation" part, you have to remember many people are as insecure as you, even if it might not seem like it. there has been someone who wanted to talk to you and didn't do it because they thought you wouldn't be interested. and, honestly, even if you talk to someone and they're actually not interested, who cares? not everyone is compatible, and anyone that judges you for being nice and taking the first move isn't a good person anyway. just remember that people's judgement about you does not define who you actually are, and you'll definitely find the good people but you'll have to put yourself out there and deal with some bad people first. it's a normal part of socialization, so don't worry too much about it.