Zofran veteren checking in! I had to take Zofran and Phenergan continuously round the clock while bf. There were no problems. I took it when pg with DD until 18 weeks pg - and still nursing DS. She's perfectly healthy and nearly 3. I took it this time around until 14 weeks pg and still nursing DS. I took it in my pregnancy before this one, which I miscarried. I was nursing both DS and DD at that time. From all I've read, it's safe. Zofran helped keep me out of the hospital, more or less. I still was too sick to function and still had an IV on occassion, but at least I didn't have to live at the hospital. There was no other option other than take meds for me or I would have died.
As far as enough nutrients for baby when you have HG, you likely will! Your milk supply may suffer first. Well, after your hydration does. My supply plummets when I get pg. My nurslings still nurse despite there not being enough to swallow pretty quickly. I still manage to grow very healthy babies. I gain back what I lose - and far, far more than average eventually. I don't take any vitamins when I have HG other than folic acid. My babies have always measured 10-14 days ahead or more by the 18-20 week ultrasound. Don't stress over your nutrition right now. Just focus on staying hydrated and trying to stay out of the hospital.