Not to scare you, but I'd check with my doc if I were you. Before I got my blood sugar under control I would sometimes have blue tinged feet, blue nails, cold hands and I felt cold all the time. I haven't had it in a year, since I started losing weight, watching my diet, exercising etc & my blood sugar stabilized. I was hypoglycemic for decades. You might also have your doc check your thyroid since a hypothyroidism can cause that as well.
__________________ "Most folks are about as happy as
they make up their minds to be."
- Abraham Lincoln
Okay, this sounds really wacky, but my tailbone hurts frequently now! Did I lose fat from my tailbone?????
Years ago I lost 40 pounds going to one of those "centers", anyway one of the reasons that I quit going (besides the astronomical cost) was that I got bruises on my behind from sitting. Yes, that's right from sitting, I was a design student so I had to sit for hours at a time on a hard uncomfortable wooden stool. This time around I'm hoping to avoid that problem by working out in such a fashion as to build-up some good solid muscle on my fanny and to never ever sit on one of those horrible stools again. So IMO it could be from losing weight, all the same you might want to have it checked by your doctor. Are you doing any stretches? Whenever my back hurts I stretch 20-30min/day and do lots of sit ups, that seems to iron it out in a day or two.