Unisom

Has anyone tried unisom for nausea? Is it safe? I am almost 12 weeks and have been occasionally using Zofran for nausea. I am trying not to take Zofran as it constipates me badly. My doc recommended Unisom a while ago. When I went to ask the pharmacist, she told me not to take it. I am confused. Is it safe? And have you ever tried it for nausea?