If you're (understandably) reluctant to take meds, it might be worth discussing how to manage the symptoms that are most debilitating.
So, enemas will help tackle the disease locally and might help then with any bleeding, diarrhoea, cramping (been a long time since I used them).
If you're struggling to keep hydrated, then anything that helps bulk you up and reduce the number of bowel movements will be useful. Rehydration salts (if permitted during pregnancy? I would assume so?) And like a pp said, go back to basics with diet. For me, that also includes upping my salt intake (my inner crisp monster loves this), and lots of potato and egg. Sports isotonic drinks at the very least?
Blood tests to check full nutrition levels - especially things like iron, b12, vit d, magnesium etc
If food is hard on your digestion rn and nutrition is an issue, then you could also discuss with your consultant whether ensure or complan drinks are worth a go.
When are you due to start maternity leave? If you're as unwell as you sound, I would think you need to take it early or at least be signed off sick for a few weeks. It's worth doing everything you can to rest and buoy up your strength before baby arrives.
It's been years since I needed treatment for a severe flare and there are new treatments now, so maybe they can treat you safely with prescription strength prebiotics as well? I don't know the effect of biologics on either your body or your baby, but I'd certainly be asking the consultant about every possible treatment route in the hope that they can be a safely used during pregnancy.