Morning sickness after 20 weeks?

I had morning sickness from week 6 until about 14. For the last month I’ve been feeling great. I stopped taking the unisom and vitamin b that was suppose to alleviate my sickness earlier (it didn’t do much). The last 5 days I’ve been back getting sick. I’m now at week 20. My concern is after my ultra sound last week the baby is only in the 15th percentile. Pretty small. My concern is if I start getting sick again and often how to get this kid to grow and put on some weight. Anyone else have an issue with morning sickness reappearing?