25mg is slightly surprising -- standard cases of situational anxiety are usually initialized at 50 mg. However, since I have no knowledge of your medical history in regards to this matter, it's best you do according to what your doctor has suggested. How old are you?
1 - I recently was prescribed 50MG Zoloft about 2 weeks ago. I'm 25 years old, and was informed by my doctor that it will take 1-2 days before I feel a noticeable change in my levels of anxiety.
2 - Taking Benadryl to stimulate restful sleep isn't a health hazard, but at the same time its NOT a very good habit either. If I were you, I would take Benadryl at night only if necessary, in the presence of actual symptoms. Zoloft can be taken during the mornings. Try to avoid taking Benadryl & Zoloft together at any point in time as both have a tendency to induce drowsiness in patients commonly -- hence two isn't better than one in this scenario.
3 - Zoloft RARELY causes any discernible side affects when prescribed in restrictive dosages. In fact, it is considered one of the safer prescriptions within the range of relaxants available on the market today. However, much like others -- prolonged usage (2 months & above) of Zoloft may culminate to one or more slightly discomforting side effects; diarrhea, short term memory loss, fatigue, lethargy, etc. However in your case assuming it's short term (for a week or two), this really isn't even a consideration.
Seek professional medical supervision in order to find out more about your case-specifics.
Question #1: They say it takes anywhere from 2-3 weeks to get into your system.
I take Lexapro. Just started back on it a week ago or so. I felt my thought process change the NEXT DAY! It's different for everyone! =)
Question #2: The only reason you should take benedryl is if you have allergies.
I know it's easy to do, b/c I'm tempted.... cause it helps me sleep. But it's not recommended to be used like that.
Question #3: Side effects? Depends on the person. It's different for EVERYONE! You may not even have any but good side effects!!! =) If you do have any side effects, just discuss them with your Dr.
Good luck. Hope I helped.