Can i take diphenhydramine at night, along with nyquil. also, if i need to, can i take klonopin with nyquil or diphenhydramine?

Your pharmacist will be able to cross check all your medicaions for possible drug drug interactions in their database. It is best to avoid diphenhydramine for the common cold. Nyquil alone is usually effective in reducing symptoms. Monitor temperature and reduce fever as indicated. A COVID 19 screening test is recommended. Watch for signs of shortness of breath and prolonged cough.