Go off for a couple of days, and do a liver flush, that might help the histimine reaction. You can also take an anti-histimine for hives (this might be enough to get me kicked off the forum, but you need to know). Hives can be very serious because they can occur internally and cause your throat to close. A histimine reaction is an immune reaction to something in your body, it could be from one of the herbs in humaworm, or it could be die off from a parasite.
Usually hives are considered symtomatic of food allergies , my daughter is severely allergic to eggs milk and soy, if she manages to find food without any of these in it, she's just fine. If not, she swells up, and if she doesn't get an antihistimine, it gets quite serious.
I would also ask RJ on the ask Humaworm forum what to do, he has a lot of experience with his forumula and it's a good one that I've used successfully myself.