@Mumtobe888 Ugh, I am SO sorry that you're not only heavily pregnant and having to look after a toddler, but that you've also found yourself saddled with a total man-child 🙄
I can literally feel my blood boiling reading the bit that you wrote about him saying that you're his mum... perhaps you ought to remind him that you're fully aware that you're DS's mum, but you're not HIS mum and he has a responsibility to your child, too. And, in fact, as your partner, who (I presume) consciously decided to procreate with you, has a duty of care to you, too. So, perhaps if he's unwilling to share the load, he can pay out of his own pocket for a childminder so that you can have a break. And, while he's at it, maybe he can also pay for a cook and a cleaner.
In the meantime, I suggest you stop doing anything for him that he can reasonably do for himself. Don't wash his clothes. Don't cook his dinner. Don't do a single thing that you don't have to. Because that seems to be exactly his attitude towards you. So, from now on, if he's not prepared to pull his weight (and, by the way, we women need to stop referring to that as "help", because it's not - it's simply him doing his part in what are essentially SHARED responsibilities), then you need to stop enabling his attitude.
And, if (when) he calls you out on it, simply remind him that, as he said, you are DS's mother. Unfortunately, however, DS happens to have an absent father and you have an absent partner, which means that you have a higher workload to contend with than you can reasonably sustain. Therefore, in order to ensure you can fulfill the role of both parents whilst maintaining your own wellbeing, you've taken the decision to stop undertaking anything that isn't geared towards caring for yourself and DS.
Failing any kind of meaningful improvement, I think you really need to weigh up your options and consider whether you can continue to live with this excuse of a man. Do you have any other family/friends who may be able to provide support after your c-section? X