OP, I have to dash in a moment, but here are some things I have found to work.
Eat little and often - your body really needs the fuel to keep going.
Chunk your days into periods of time - 10 minutes, an hour, whatever you feel you can manage, and give yourself a pat on the back everytime you get through another chunk.
Change things around a bit so that you take some empowerment back. Could you get a new duvet cover, move the furniture, paint a wall?
Change your habits. If you always went to the same pub on a Friday, go somewhere else. If you always shopped in Tesco on a Saturday morning, spend Saturday morning watching a movie, and go to Sainsburys on Saturday afternoon instead.
Speak to your friends, and build a support network. Even if that means chatting on the phone for hours. But choose them wisely - not gossips, or people who will just get down the well with you - try to find those people who will help you pick yourself back up, rather than keeping you feeling down by going over and over the story.
Think back to what your dreams were before you met your ex. What did you want to do/be? Can you do any of that now?
Ask yourself what you can best do to support yourself. Be kind to yourself. If you love flowers, buy a bunch on the way home, if you like a hot bath, take one.
Flip things around, so that you find the chink of hope or light in the situation. What did your ex get irritated by that you can now do whenever you like?
Also look for things to feel glad about or grateful for. Even if it's just that the sun is shining! Our brains have a negative bias, so it's easier to hang onto negative emotions than it is to focus on positive ones. It might be an effort or feel forced at first, but trying to find the positive really does work.
And lastly, let yourself feel your emotions. Don't be afraid of them, they are there for a reason, to let your body know it's hurt. So if you want to cry, cry. There is a grief process to go through at the end of a relationship, and it's important to feel your grief. Just make sure that you also start to notice when you are feeling something good too.
Take care. x