I take 50mg of trazadone/day. I'm also dealing w/seasonal allergies. What can I safely take? Robitussin? Benadryl (diphenhydramine)? Everything carries warnings.

Nasal steroid spray. Nasal steroid sprays are the most effective treatment for seasonal allergies. In addition, there would be no drug interaction with other medications including trazadone.
Any/all. You are on a low dose of trazadone--all the drugs you listed cause drowsiness--take the trazadone 2 hrs before bedtime & you should be ok.