Diphenhydramine in OTC Sleep Aid Supplement

[svt2001]

I use 25mg diphenhydramine (Benadryl) on a nightly basis coupled with melatonin and GABA to help me sleep. I couldn't live without it. Can one use diphenhydramine to make a supplement since it is OTC or is it illegal to do so? I'm just surprised that no one has done it since it's so effective.