Dr Blake's comment: Typically achilles tendinitis is an overuse injury, so your description of being stepped on makes it harder to get a read on. Putting yourself in the Immobilization Phase was the right idea, and it should be coupled with anti-inflammatory treatments as well.
Dr Blake's comment: Bursitis in front or behind the achilles is a common side effect of achilles tendinitis swelling, or the bursitis was the only source of pain from the beginning. Bursae are fluid filled sacs that collect fluid in the wrong place and act as an irritant to the surrounding tissue. Bursitis elsewhere is treated with cortisone shots, but these are risky close to the achilles. I prefer electrical stimulation with contrasts, or iontophoresis, while going to PT.
He checked by strength and noted that my left gluteus (it is the left achilles that is the problem) was weak. My trainers switched up my strengthening program to include more gluteus exercises to improve this.