I totally understand how hard it is hun
After my DD was like this I thought I surely couldn't get another....but yep DS is worse! Like you often i question whether or not I have 'caused' it. But my sensible brain tells me that some children are just like that.
FWIW my DD is now a friendly (sometimes too much) outgoing child at nearly 4. I keep myself hanging in there by telling myself that they are seeking security and to start I am their whole world. My giving them extra security is just building up their confidence slowly and making them secure in themselves.
CC can threaten the strongest of children.
It will pass, you are doing a wonderful job.