When homeschooling gets hard! Stop !

These past couple of days homeschooling has become pretty hard. I never thought it would be easy but my son seems to not want to o anything at all. None of the games, he doesn't want to go out really, he just wants to play with cars. I think learning can come from all places. However, I don't think he is learning anything throwing cars around the room. I tried to turn it into a learning game but he does not want to know. I did five minutes with him this morning before I burst into tears. What is the solution ? Stop ! I am just going to leave him to it for the next few days. Then try again, this is the problem they had when he was at school he did not engage, even with the fun stuff. He seems to have gone backwards in this past couple of days. 

He was flying last week, now he doesn't know his numbers or letters anymore. I am not trying to force him but I want him to get the basics down before throwing a whole heap of other stuff on him. I thought he was interested in science but he doesn't seem bothered about it. I know he is only 4 so I shouldn't push him but I am running out of ideas at the moment. I have to rethink, sit back and rethink.