My doc said 12.5 mg every 6 hours. I know it was 12.5 since I had to cut the pills in half. I found vitamin B6 to help more (25 mg every 6 hours) since I took that alone during the day and with unisom at night. I got a prescription for zofran this time due to severe nausea - you might want to consider it if you're having that much trouble.
Some doctors will OK unisom during pregnancy; it's essentially Benedryl (with the same active ingredient)...however...I BELIEVE that you are far exceeding the dose, and you need to call your OB the minute they open tomorrow morning and make sure you're not putting the baby in danger.
Even doctors who OK it generally tell you to use as little as possible, as infrequently as possible...so taking as much as you are every single night might be best avoided....you need to speak to your doctor about the dose ASAP.
I'm pretty sure you're not supposed to be taking that, have you asked your OB about it? The first trimester is the period where a lot of critical development happens, so if you haven't been told it was safe I'd definitely stop taking it.