Unfortunately, as an independent contract, you have very little recourse.
Any advice offered does not create a laywer-client relationship. If you require legal advice, you should seek an attorney, licensed to practice in your jurisdiction and in good standing with your state bar association. You should not rely on the advice posted herein due to the limited nature of information available about your inquiry.
Generally, there is no obligation to renew an employment contract. However, if the reason you gave and your suggestion that the refusal to renew was health-based your rights *may* have violate your rights. You should be able to get a free initial consult with one or two employment lawyers for free in your area of the state.