I have no idea about any natural remedies, as I never suffered from it. I suppose those who were affected would have asked about or researched this. Mothers groups and maternal health nurse would be able to advise on this also. Maybe herbal teas? Vitamins or herbs? Ask a professional or Google it.
My sister's doctor told her to eat a small piece of cheese as it was protein that the body was asking for. Mine didn't last terribly long so I never really used anything. I feel so sorry for the poor girls who are sick throughout their pregnancies.
My GP suggested nibbling crackers slowly to settle my stomach, though I didn't have a lot of trouble with morning sickness anyway. I've heard some people drink ginger tea for it. I notice the question is tagged "hyperemesis Gravidarum". That's not morning sickness, it's way more serious, and might need medication or even hospitalisation.
I suffered for almost the entire time during my second pregnancy but not so much with the first. I found the only way to overcome it was to stay in bed all day. My husband would leave me some dry sao biscuits and water until he came home and cooked dinner with the bedroom door closed. This way no smells could set me off. Mum would come down from the Central Coast and stay a couple of weeks to give hubby a break. My stainless steel sink was spotless and shiny but I couldn't walk out into the kitchen and look at it without heaving so eventually I was hospitalised and that helped until I had the baby.
Vitamin B6 tablets with ginger and protein rich diet helped me a lot. Some people swear by ginger tea as well. But if you have something like Hyperemesis gravidarum, none of these can help ! In that case, one definitely needs a doctor's help.
If you're going to get full blown hyperemisis there's no cure for that, it's HORRIBLE. I had it with my first and it's a wonder I'm still here I tell you. I started pregnancy at 50kg, and 12w later I was 38kg ..... and the hospital sent me home and told me to drink more water.
I had crazy morning/afternoon/evening sickness! Once I was interviewing an elderly business woman for an article. she watched me while I was struggling to take notes while running to the toilet ever so often. She mixed coke and water and got me to drink it. It did help with the morning sickness and I finished off the interview uninterrupted there after.
The best thing that got me through each time was soda crackers and gingerale. The soda crackers will also help with heartburn. I had morning sickness for more than seven months with each of little ones, good luck.