You said it's not fear, but then you said you don't want others to know that you don't know, which is a result of fear of judgement. No one will give you the enough time to say what you want. This is called life. It's an arena. You need to prove yourself somehow. You need to squeeze yourself in a conversation whenever you have something to say and at the most appropriate time you get, like at the end of a sentence. If you feel you interrupted someone, say "sorry for interruption, but ..." and proceed. Again, I relate to you in this, too. I've considered the possibility of Asperger myself, but it doesn't seem that I miss social cues, and that I can't read people's intentions. If you feel your family isn't supportive for you, try CBT books. Just to get insights if it's applied to you, which seems likely. Do you have problems making eye contacts with people?

Try this book.