Not many people consider benzos to be euphoric, and mistake a feeling of relief (like the relief from anxiety) with euphoria. You could be experiencing something similar. Some sort of relief from the symptoms that your diagnosed disorder has, from using the thorazine.
If you are concerned about the dosage of your medication, you need to talk to your doctor. We don't know your medical situation, nor are doctors treating you. If you feel your medication or dosage needs to be adjusted talk to your doctor. Also, if you are concerned about medicine reactions, like how benadryl may be reacting with the thorazine, talk to your doctor.
May I ask why you are talking benadryl? I honestly would avoid benadryl (diphenhydramine) if I was taking anti-psychotics like thorazine because of both drugs ability to produce tics and exacerbate nasty body movement related disorders
Also if you have Schizoaffective disorder you really shouldn't be using drugs recreationally.