Who's responsible for worker's compensation?

I have been at my present job for 3 months. I have been experiencing pain and numbing in my hands and lower arm. I believe it could possibly be carpal tunnels. I would like to be check by my works doctor, but I'm not sure if they will be required to cover considering that carpal tunnels develops over a long period of time. I have had several jobs in Wisconsin in the last three years. The job I am at now mostly involves pulling orders and shipping them out. Am I going to have to take care of this problem on my own, with my own expenses, or will workers compensation cover it, even if it is possible that one of my other jobs was the main cause for my problems?

The first thing to do is let your present employer know that you have been experiencing pain and numbing in your hands. Have them send you to be evaluated. It's possible you have tendinitis, which is not as serious as CTS. If the injury is due to your present employment, they are on the hook for your claim. If it is something that has been ongoing, prior to this employment, but you're just now determining that it's work related, your previous employer could be on the hook, OR there could be what is called aportionment. That is where it is determined that the injury did not occur under your present employer, but your work with them did contribute to the injury. Therefore, both employers are liable and the claim is "portioned" out.