Signed off work with stress because of my toddler

I am pregnant with my second and I have been signed off work with stress because of persistent tension headaches and palpations. It has nothing to do with the pregnancy and everything to do with my toddler. Yes, this is a rant.

My daughter is 2.5 and is plagued with health issues that are completely self inflicted. She will not even attempt to take the slightest care of herself. She won't drink any liquids (not water, juice, not milk, nothing) or eat enough food no matter what I put in front of her unless it's chocolate, so she's constantly very constipated and has a sore throat which she then complains about endlessly. I try to explain that she needs to eat and drink otherwise she'll be unwell but she doesn't listen. I'm sat there every night giving her stool softeners and suppositories but she is still withholding her poop and making it worse.

So she won't eat. She won't drink. She won't even poop.

My question is: how am I supposed to fulfill my responsibilities as a parent when my toddler is refusing to engage with even the most basic biological processes of her body? Even newborn babies and single celled organisms know that they need to eat and s**t as an absolute minimum but even this is too much for her. I am feeling increasingly frustrated and angry with her. I literally cannot do this stuff for her. I can provide food and water but I can't make her eat and drink it, yet I am still the one having to deal with her poor health when she feels like crap because of her own choices. I'm the one sat listening to her cry for hours because her tummy hurts. I'm the one being woken up at 4am because of a sore throat caused by dehydration.

It makes me feel like why should I bother trying as hard as I do to accommodate her and look after her when she won't fulfil her end of the bargain? On purpose? Not due to disability but just... Because she doesn't feel like it?

I wish I'd never gotten pregnant again. I never want another child in case they're like her.