I went through this same exact thing over the weekend! Sitting at work on Thursday afternoon, I moved and it felt like an area on my breast hurt. I went to the bathroom, felt around & sure enough it was tender in one area. Instant panic & fear of breast cancer ensued, as did the constant poking, prodding, pushing & what ever else I could do to try & make the pain disappear. That night I continued with the constant pushing on it, poking, prodding, comparing it to the other one & then started the God forsaken googling to find out what this could be with the inevitable, all signs pointing to breast cancer. The internet is an evil tool when it comes to health concerns, I swear you can google headache & end up self diagnosing a brain tumor! Needless to say, not only did my breast hurt, but now my head & stomach did as well from the worry & thinking I was doomed! Saturday I spent all day stressed out, my stomach in knots until I literally was sick. I did know "that time of the month" was coming soon so was trying to believe that it was hormonal since I do normally get breast tenderness before I start, however normally it's in both and not just one & not just one isolated spot. I too had poked so much I bruised them both. This morning when I woke up, I noticed the pain had dissipated some what & was thanking God!! This evening after I got home from a meeting & was able to resume my never ending poking & prodding, I noticed the pain was almost gone & upon visiting the bathroom I noticed I'd "started". So I'm attributing it to hormonal cyclical pain & hoping that's all it is.
From all that I read, and I read a lot it said breast pain is not a common or typical symptom of breast cancer. Breasts can be very lumpy, the breast tissue itself can be.
I hope I helped relieve you a little bit.