Deciding whether or not to hire an attorney can be a tough decision. Most will tell you that you will do better when you have an attorney handling the claims, and I agree in most cases. Some are small enough that hiring an attorney may not be the most prudent decision.
The fact that you have been in two collisions pretty close together following medical treatment to an area that is the most likely to be injured in a rear-end collision complicates things. Obviously the adjusters from both collisions will want to point to your pre-existing collision as the reason you needed treatment post collisions. They will also point the finger at each other as the one most responsible for post collision treatment.
Given those complications, you probably need an attorney’s assistance more than most. If you do decide to hire an attorney, make sure you are comfortable with their communication style and that they are setting reasonable expectations.