Oh looooove, I'm so sorry you're going through this.
First of all, noone gets a 2:2 by accident. You did really well, especially considering that you were so afraid of seminars and presentations. You should feel proud of what you have achieved. You are in no way a fraud.
I think a LOT of people's success honestly comes down to front. I would be willing to bet a lot of money that you haven't had the confidence to put yourself forward for jobs for which you are eminently qualified. You probably really fear rejection, and always think someone else will do a better job than you could. Those thoughts aren't really true, but they are materially crippling your chances. Some of this often comes down to background - people who have grown up working or lower middle class often don't put themselves forward with as much front as those from wealthier backgrounds, often because they've been told repeatedly how they won't amount of anything (there was a very interesting thread about this over the last few days).
It sounds to me like you're also dealing with an extremely undermining family, which can do enormous damage to the self-esteem and confidence of people from any class.
It can be easy when you feel this way to retreat into a limbo - taking work on that is easy, and hiding from everything. But that's not really the way to be happy. It just temporarily dulls the pain. (Doing easy work because you LOVE IT is totally different and affirmative).
I think you would benefit tremendously from a combination of life coaching and counselling, ideally from the same person. There is clearly a mental pattern of thought here that is just destroying you. Please listen to me when I say it doesn't have to be this way and there are much more positive ways in which you can think about yourself that will allow you to take on more.
I can relate to your post. I have a PhD but have never come anywhere close to achieving my potential, for similar reasons of utter confidence shock. Thanks to counselling, I've started going for things. In my early 40s, I'm about to publish my first book with a major popular publisher, I've got a research job, and people are actually inviting me to speak and edit things. You still have loads of time to turn this around. Find some appropriate support, and you will boss this.