My first inclination is that its fine, and being caused by the muscles in your body learning all about your new vagina. Vaginoplasty creates a vagina by going through muscles, so I would expect that it is these muscles that are being troublesome. I would not worry too much, but mention it to your surgeon when you can. I can ask Dr. McGinn about this as well, I will be speaking to her on Sunday probably.
Do not stop dilating.
Update: Blood and tissue discharge on the dilator is normal (the more granulization tissue in the vagina the more blood there will be). Pain is normal. Make sure you are getting under the pubic bone and use as much lube as necessary o..o
Update 2: You might try massaging the muscles with a finger or two in the vagina or from the top, outside (whichever is closer). Apply firm, non-forceable pressure to the area of pain for 3-5 minutes and try to let the muscle relax.