My heart goes out to you. I recognized myself in your note. It is hard to have to hold yourself together when you are depressed and can't get relief. I agree with the writer above, who said to take time for yourself each day and to be good to yourself. I would go so far as to say to indulge yourself. Whatever gives you happiness, indulge in it. If you are in a doctoral program [which I have done, myself] you are already under an enormous amount of stress.
I find that writing positive affirmations helps me. Sometimes it is really hard to do, but it is a good exercise and it does help. Then, when you are feeling really low, you can re-read them. I hope you start feeling better soon. You sound like a phenomenal person. Keep reminding yourself of that fact.