In the past few years, blockchain has proven its necessity and unprecedented prospects in providing a secure environment for information exchange between two parties. The integration of the Internet of Things (IoT) with blockchain has enabled a digital transformation in many areas such as healthcare, supply chain, and financial services. Like blockchain, the programmable Software-Defined Network (SDN) is also achieving popularity due to its ability to reduce network management complexity. It is evident that incorporating SDNs with IoT-based healthcare systems can significantly improve healthcare management services. However, there are a number of challenges such as data confidentiality, user-centric design, integrity and privacy that makes it difficult to share sensitive information among different parties in a healthcare system. To overcome these challenges, we propose an architectural framework that incorporates blockchain with Software-Defined Wireless Body Area Networks (SDWBANs) to facilitate secure data sharing. We have also designed and integrated a smart contract based fine-grained access control policy to ensure that only data owners will have full control over their health data. The experimental outcomes show that the proposed model achieves good throughput and incurs a very low overhead in terms of latency compared to traditional cloud-based systems.