If you're going to ask for medical advice on a public forum - which is ill-advised, at best - you ought to at least supply enough information for someone to hazard an educated guess. For example, what kind of antidepressant are you on? If it's an MAO inhibitor type, then taking Benadryl along with it could be very bad, indeed.

My advice to you is to ask your physician. Or at least a a physician or even a pharmacist. Taking anyone else's medical advice is just asking for trouble. When it comes to your health, don't fuck around.