Had an ITB on my right leg about a month and a half ago. Came out of the blue, but possibly due to increasing volume on the bike too rapidly.
Same symptoms as you - hard to walk, put pressure on the leg, etc. Drove me crazy!
What has worked for me:
Tissue massaging - roller, ITB stretches, and most importantly this one: http://cyclingphysio.com/wonton.html
Dead serious, it helped a ton (no affiation)!
Re-examined bike fit - lowered saddle height, changed cleat rotation angle to suit the "rest" angles of the feet (mine a "toes out"). Also switched to shorter cranks (175 -> 170mm, and I'm 185cm), in order to reduce the range of knee flexion. Can't say if the crank change helped with the ITB, but it hasn't been back since...knock on wood.
Glute muscle strengthening exercises - I do them daily now. Some examples here: http://cyclingphysio.com/exercises.html
Good luck getting over this and I hope it goes away soon.