Recurring raised white welt on forearm?

Hello everyone!

I work in a group home and I've noticed a few separate times that when I'm at work, a raised white welt the size of a dime will appear on my forearm.  It lasts for a couple hours and then leaves.  It almost looks like something was injected into my arm and is reminiscent of when I had a bad reaction to a TB test.  It occurs in the same place and always looks the same.  I'm not sure if the fact that it happens at work is a sign of an allergic reaction or just a coincidence, but usually when I get hives, it's a red, itchy rash.  This bump is not itchy or red, just a white raised area with no other symptoms.

Any idea of what this could be?  I wasn't concerned the first time it happened, but the fact that it is the same bump reoccurring is a little troublesome to me, although I'm sure it's not anything major.

Thanks!

[jenbob555]

Edit:

I now have a couple on my other arm, as well as the original bump and they all turned up while I was in class, not work, making this even more confusing.  Does anyone have ANY idea?  I can't go to the doctor as I don't have money for insurance.