I've solicited some advice (some of it here) and done some reading, and have started adding two supplements to my diet. Creatinine and Pyruvate. I don't know if it was them, or just purely an adjustment to regular exercise, or what, but something was different. My arms and chest and back didn't "catch fire" this time, at least till the end, at which point it wasn't nearly as bad, and I wasn't nearly so sore immediately after. We'll see what tomorrow morning is like.
I'm losing about a pound a day (I was 234.5 last week, and this afternoon I was 227.5). That's ok this early in, but it's on the edge of being too fast. And it's not dehydration either, I drink about 3 liters of water per seated "office shift", and over 1.5 liters each gym session.