Benadryl (or Diphenhydramine) is listed as one of the medications that could be taken during pregnancy. https://www.pharmacy.nhg.com.sg/page.aspx?id=684 It is commonly used as an antihistamine for minor cold and flu symptoms. It may cause drowsiness but is harmless to you or your baby. However, do consult your doctor for appropriate dosage. For more information on this medication: http://www.pregmed.org/benadryl-during-pregnancy.htm
Benadryl is usually considered safe to take when pregnant but be sure to check with your doctor before taking any medicine.