Tailbone or Coccyx when Deadlifting

Good Morning,

Male, 36 years old, 6ft tall, 220lbs, still a novice
Current Lifts:
Squat: 310lbs
Bench: 220lbs
Dead: 345lbs

Back Story: A few weeks ago while following the linear progression, I performed my first rep deadlift for the day at 375lbs when I felt an excruciating pain around my tail bone. I lowered the weight and collapsed, and was unable to walk for about 24 hours, and it took a week before I could walk pain free. It hurt like hell to take a shit or even piss! Since then I have re-started my linear progress back at 225, increasing by 10lb increments to 345 as of Friday.

I have found that widening my stance to just wider that shoulder width completely alleviates the pain. A narrower stance causes me mild pain in the area even down at 225lbs, enough to deter me from pushing the envelope.

Am I screwing up by widening my stance? What are the consequences? Should I be doing something different to prevent this type of injury?

-Joshua