What Causes Breast Pain And Arm Pain After Taking Doxycycline Hyclate?

My daughter is 15 1/2. She is only 4 10 , and around 90 lbs. She has been trying out for soccer this week, so she has had more physical exercise than normal this week. She came home today complaining of pain in her left breast, sometimes she gets a sharp pain. She also said that her left arm hurts on the underside of her arm, and that her arm felt somewhat limp today. I ve taken her blood pressure and pulse in both arms. Right: BP 87/54 P 61, Left: BP 83/53 P 62. She is currently taking Doxycycline Hyclate 20 mg, 1 tablet twice daily for acne, and Dexmethylphenidate (Focalin) 5 mg 1 capsule 1 time per day. Her left breast does appear slightly swollen. She says that she doesn t recall getting hit during practice this week. What could this be?