Didn't want to leave your message unanswered.
You sound like you're having a really tough time 
I think it's completely understandable to be reeling from the news and want support from your family. Can you talk to them again and explain how you feel like you've done here?
If they're advising a hysterectomy are you under the care of a gynecologist? If so they can usually refer you for 'fertility' counseling (i.e. A counselor who specializes in the practical and emotional aspects of infertility). Even without a womb you have options in the future (surrogacy etc?)
Anyway, without trying to sound patronizing you are 21, you have many years to explore your options..... I think intentionally engaging on a plan to get pregnant with a ONS while you are facing multiple serious health conditions, would have no partner to support you, no where to live, no job, no family support and be trying to do higher education at the same time is lunacy!! How do you genuinely think this will actually work?
Babies need more than just love. Yes they don't need lots of 'stuff' (toys, expensive Prams etc) but they need somewhere to live and money for heating/food/nappies etc.....
Not to mention how unfair it would be to the child to intentionally 'make' their father a ONS and probably absent parent.
I understand that thinking you're ok with something but then actually having to face the stark reality is a massive shock. I understand the pain of fertility issues.
But this is a terrible idea. Knee jerk and - gosh I'm going to sound like a heartless cow - but quite selfish and irresponsible.
I would really recommend seeking some real life support. Can you talk to your family again? Do you have specialist nurse support? Autoimmune specialist nurses will be used to helping women with fertility problems.