Welcome here to the Forum. It can be a hard thing to open up, even here where it is anonymous, so I'd like to say you have done a pretty brave and sensible thing. Here you can get other's views, and there are no worries in the process. You are quite right, it is a first step.
Feeling like you might hurt others does show a very caring side to your nature, and that combined with a reluctance to talk about deep matters - understandable in the circumstances - has left you discovering you are hurting yourself. Do you have any idea what started to give you the notion you might hurt others by saying what you thought?
That stony faced mask too is not good. We all have one to some extent, but when it is too effective it hurts the wearer. I found when I hid everything it simply isolated me. I was not able to be with others in comfort, plus I got the feeling if I had to hide how I realy was - what did that say about the real me? Perhaps you feel a bit the same?
It looks like things are gettng worse if I understand right. Constant disappointment, loss of ability to enjoy, finding tasks difficult, wanting to just hide. Plus not wanting to wake up for another day the same. Now you want to avoid physical contact. Upsetting how things can get worse.
It does not really matter if on the outside it looks like you have a good life, it is how you are inside that is important. To feel this way is not something to be ashamed about, after all it is not something you chose.
Can I suggest you get some help? I found I simply was unable to improve without that help. I ended up with medications (which I needed, you may not) and therapy, and it turned my life around -not the next day, but in time. I'm not the same person now. Apart from other things I can now be with others, talk openly and enjoy it, plus others appreciate what I say - quite a surprise after how I felt.
Life can be so much better, you do not have to keep on going like this.
So what to do? The are several options. If you wanted you could talk to your parents, I don't know if you felt able, but it is a suggestion. If you are at school there may be a councilor you can trust and have confidence in. If you do not want face-to-face there is
The Kids Help Line, by phone on 1800 55 1800, or by web-chat at https://kidshelpline.com.au
You are not alone in this, we are here for you whenever you like