The biggest concern I can think of is dehydration with epson salts. It's a problem for people who aren't pregnant so it might be worse being pregnant. You'd have to drink a lot of water the day before and the day of the flush. Also sip some water before and after the epsons as needed if you feel yourself getting dehydrated.
I would think there might be a problem with toxins going to the baby.. But with what you're feeling now, you're toxic anyway and your liver is clogged/overloaded. So I don't see how it's any worse..at least with flushing you'll be ridding yourself of some toxins.