Welcome to beyond blue. Most of the users on the forums are you and me. We are not professional in mental health. One of the things that binds us together may be depression and anxiety, so remember that in this space you are not alone.
I can also understand some of the feeling that you have - being snappy, not wanting to apologize, being constantly on edge, etc. For myself, the things I have copied from your post are symptoms of depression and anxiety (and haemochromatosis). In fact, constantly being tense and on edge, or easily started is related to anxiety (at least for me).
I guess the first question is whether you have been able to speak about this with your parents? or a friend?
Perhaps you could also check out the K10 test on the beyond blue website? It is a small test and will give you a recommendation at the end as to what action (if any) to take. For example, it might suggest talking to a GP? If you got that recommendation would you be able to follow through?
Your mood might also be side-effect of how you are sleeping. Again that is what I found. So I wonder if you are tired in the day time? Are you able to sleep through the night? Or do you wake up? And think about things?
There are many factors that play into how we feel and the (re-)act toward others. You might want to have a look at the threads on the forum about grounding and mindfulness. In these threads you might find some ideas to help you relax etc. However, this will not help you with not apologizing. Which leads me the question...
You said that you recognise when you do thing wrong, but are unable to apologize. What are you afraid of if you were to say "sorry" to your parents if/when you did something wrong?
You don't have to answer that question here, but it might help you to work out the cause, and then be able the work on that to find a way forward.
Peace and best wishes,