My baby is ten months old. I nurse 1-2 times a day, usually just once in the morning. I still have not had a period. Should I be concerned?

Depends. It is possible that breastfeeding has continued to keep you from ovulating and having periods. But, it is possible to get pregnant while breastfeeding. If you have not taken a pregnancy test, you should consider it if there is a possibility of pregnancy.
Nursing amenorrhea. No need to worry at all. Breast feeding is a well-known cause of delayed resumption of regular periods after childbirth. In fact, in some parts of the world, this effect is a common means of birth control. It is not recommended for this use, however, since it is not sufficiently reliable.