Is this normal or I am like becoming mentally unstable?

I think that you are suffering from depression personally. Being irritable can be a sign of depression so I would recommend seeing a doctor and describing your symptoms - exactly like you've done here - and then they'll be able to help you the best they can. Being depressed isn't a life sentence and with maybe taking anti depressants for a little while you'll be able to start functioning normally again and not need them long term. But I'm not a doctor. So that's why I'm recommending that you see one. Hope this helps :)