I've had issues with Crohn's-related intermediate uveitis for a while now. I saw an eye doctor about it when my symptoms started (excessive floaters, flashes in vision) and said he could see the floaters, but referred me to a retina specialist for diagnosis. I remember my symptoms weren't so bad when they first started, but then after a little while (probably about a week or so) they got worse... more floaters, more frequent flashes. So it may just be a coincidence that your symptoms worsened when you started Humira. I just started Humira a little over a month ago and my uveitis didn't seem to be affected. Of course, as we know, everyone's different.
Anyway, the retina specialist will probably be able to tell you more, but I would assume it's uveitis. It's a common problem for people with Crohn's. Good luck with your appointment on Thursday.