OP, it might be hard now, but it should be for a set period of time until DC is out of childcare and at school.
It's hard but you have to grit your teeth and get through it. You are playing the long game. I have been there as a single parent with no income and a £700 mortgage. I had to work hard and build my business up to a full time income. Things were tight for a while, caravan holidays, hardly any clothes for myself, no haircuts etc.
You have a house, an asset that you are paying for.
Things might be tight for a while but that is life for a lot of people unfortunately. You are allowed to feel sorry for yourself, but you need to be proactive and look at ways of saving money.
Download the MSE budget planner and enter everything on there that you spend out in a month and also enter annual costs like birthdays and events etc. Look at what is essential, what is needed and which is neither, which makes it a luxury and therefore can go. Can you switch to own brands for anything, can you buy less of anything. Allow yourself a couple of treats obviously.
You don't need clothes every month and if DC does as they grow, they can be bought cheaply in supermarkets and Primark etc.
You should be able to afford a day out.