Sick -Phenergan

Elizabeth.
Hey guys. 
I'm only 6 weeks and so sick all day long. My doctor prescribed me Phenergan And it's helped but oh my goodness -I am exhausted. I could sleep through the day! Drowsyness can occur. 
I have the topical cream, but it doesn't work as well.... Am I just going to be tired regardless so just take it? 😥