This is absolutely a question you will want to ask your doctor. Both of these substances increase sleepiness so I would think that you would have more sedation than normal.
The University of Maryland Medical Center has some good information about insomnia medications and supplements.
I personally have taken melatonin with benadryl as the melatonin gets me to sleep and benadryl keeps me asleep. But do not take these together without first consulting with your doctor. Be safe and ask first.
Thank you for your question.