Am I at fault if I'm hit from behind causing my vehicle to hit another vehicle?

no

The person behind you should not be tailgating (even though many people still do this today). It also depends on how close you are to the front of the car. In this circumstance, you are not at fault. The tailgater is At Fault. For a reminder, always keep a distance at low or high speeds. Tailgating is one of the top causes of car accidents. Stay safe out there.