I had it with my son from 7 weeks and it didn't go away completely until 16 weeks. I also had it with both of my MCs from 5 weeks onward. It was miserable. I drank a lot of protein shakes and ginger tea because I couldn't eat anything or else I felt like I was going to throw it back up. This was not your usual morning sickness... this was 24/7 nausea. On top of it, I had bad heartburn, which didn't help my stomach, and every single time I tried to take antacids for the heartburn, they would just come right back up. Every. Single. Time.
My midwife put me on Zofran with my last two pregnancies. I cut the pills into quarters and took a quarter before a meal to help me eat. I tried to steer away from the full dosage of 2 pills per day if I could because it gave me bad constipation.