Yes, I've had a similar experience. My mammo and automated ultrasound showed nothing. But a subsequent MRI found 4 suspicious areas, 2 of which turned out to be Stage 1 cancer (one was lobular, the other ductal). If a woman has dense breasts, often cancer goes undetected by a mammogram. MRI is more sensitive for those of us with dense breasts.
Try not to worry. It's good that your doctor is pursuing the diagnosis. I ended up having 4 lumpectomies one year ago and then radiation (which by the way is easy), and so far so good. It's not the end of the world, just a detour. God love you.