Horrible Tooth Pain and Turning Gray?

My tooth is SO sensitive right now- anytime I eat or drink anything, a huge stinging pain goes in between two of my teeth and all the way down. It is so painful. That tooth has also started turning grey near the gum. I made an appointment with my dentist , but this has been happening for a couple weeks. I'm scared ill have to have a root canal, and I am 8 months pregnant right now :( what do you think is happening??