from what I've read it can feel like a bruise to an intense pain, It would be a centralized spot, the spot might be red, you may have swelling, those are the symptoms for a DVT or blood clot in one of your limbs, there are also pulmanary embolisums which are blood clots in the lungs, those cause shortness of breath and chest pain, and a stroke is a blood clot in the brain, so you could have slurred speech, lose control of you limbs, have a droopy one slide of your face, forget how to talk. All of these things can be caused by birth control pills, you at a higher risk if you are over 35 and/or a smoker. I'd say if you even think you might have any of these symptoms go to the doctor, better safe than sorry.