K.D.
A friend of mine told me that she had a procedure (I don't recall the name and it's an in-office procedure) that she had because her periods were so heavy. She said they basically do something to the lining of the uterus and you never get a period again. Obviously you have to be finished having children and you are since your tubes are tied. She said you get the symptoms of a period (hormonal changes, cramps, sore breasts, etc) but you just never bleed. Maybe you should check with your doctor about it.
About the sore nipple, it could be that your baby is just not latching on correctly on that side. It also may not be cracked or infected, but it could possibly be heading there. I would just watch her latch and make sure she's taking in enough breast tissue. Also make sure she's not "slipping" as she she nurses so at the end of feeding, she's basically just got your nipple. My daughter did that and I had sore nipples from it, but as soon as I made she she was "staying put" things got better in less than 24 hrs. If it's not that, then talk to your doctor or a lactation consultant.