That is such a hard place to be. I would suggest getting a few very thin long sleeve shirts. That is what I did. I wore those, sunscreen and a hat in my office. You will be surprised how much the hat helps. I too kept a fan on myself and I always took my breaks outside. I also spoke to my boss about taking 3 5 min breaks instead of 1 15 min. break in the morning. It worked out so that I was able to take an outside cool down break about 7 times a day (3 in the morning... lunch time.. and 3 in the afternoon).
Hopefully some of that will help you.