all types of birth control are not 100% that's why if it's 99.9% affective, 1/1000 women could get pregnant while on it. So it could very well be that you are pregnant, and it could be to early to tell. Good luck on your blood test, I hope all goes well and they can understand what happened/is happening.
Just a shot in the dark, but your sore breasts could be from sleeping wrong or even over working chest muscles. I've slept on my breasts wrong for about a week straight until I finally got another pillow, then it was fine. Sore breasts is not a sure sign of pregnancy, and neither is constipation and headaches.
Again Good luck, I hope you get everything sorted out.