Hello~Did you eat any food prior that were blackish in color? If not, I would go to your ER and have this checked out, the fact that your chest and back hurts along with this causes me concern. It may be nothing, but again, it may be something that needs attention ASAP.
Please let us know how it goes.
Ash, your OB/GYN is on call. Have you connected with them?
Im not a doctor but I often cough phlegm with black/grey bits in mainly when I have a cold/flu. I was a x smoker for 14 years so am aware that my lungs probably have a lining of black tar and yukky stuff that is conteibuting to it.
If you have stomach/back pain afrer being sick that is probably the cause but as others have said if in doubt gwt it checked out