Here in Australia, on the box it says you can take up to 100mg for insomnia. So 3 or 4 of your tablets might be okay. You could call your pharmacist and ask?
I took 100mg of Benadryl a night for years and years. I can't vouch for it's safety at that dose, but I feel I should warn you, taking that much feels awwwwwful. I can barely stand and get horribly uncoordinated, so please make sure you're safely in bed before it hits you. Also don't take more than that, you can get psychotic and have a heart attack if you take too much. Benadryl can be dangerous, be careful with it. Ask your pharmacist. Oh, and you might oversleep like a bear in hibernation, so set 15 alarms if you need to be up on time.
However, it was the only thing that could make me sleep and not be a complete zombie the next day (Seroquel, I'm talking about you).