i do sympathise with you. i, too, have a staffy x and she had a load of (minor) problems when we first got her. it was a very difficult and upsetting time and i wanted to return her after the first week !!
but 3 years later, we have the most adorable, loving little girl you could ever wish for. we've overcome most of the problems she had or have got them to an acceptable level, however, there was no magic cure. it has taken a lot of time, patience and perseverance.
it can't be easy for you as a single parent, christmas coming up etc but if you want to try and improve things, not just for you but for your dog as well, then listen to the advice from the good folk on here and try and put it into practice. don't be afraid to ask more questions, you will get a lot of help and support, if people can see that you're trying but things aren't going well.
i'm sure that if you're prepared to put the effort in, then you'll be succesful. it's difficult, i know, with young children as well but i'm afraid there's no quick fix.