Device-to-Device (D2D) communication is designed to offload the traffic on the 5G core networks and backhaul links in an effort to deal with the high volume and variety of data traffic anticipated in 5G networks. D2D communications provide faster and energy-efficient access to the devices within a cell. However, efficient provision of D2D communication presents several challenges, including multi-hop routing to the devices that are not immediate neighbours to each other. Dynamic Source Routing (DSR) is a popular protocol commonly applied to Mobile Ad hoc Networks (MANET); however, its direct application in 5G D2D environment is not straightforward. In this paper, a new multi-hop routing protocol for D2D communications in 5G network is proposed. The protocol modifies the conventional DSR protocol and takes advantages of 5G cellular infrastructure to make routing decisions faster. The proposed protocol offers low overhead over the conventional DSR, in terms of the number of control messages exchanged in the D2D communication, thus saving time and energy for the devices during the route discovery process. Simulation results show that the proposed protocol also achieves better results in terms of D2D routing success probability.