YOOOOOOOOOOOO I HAD THE SAME THING LAST YEAR!!!
Thank God it wasn't just me!
I'm not quite sure how "normal" it is, but I assure you, it will go away! Kinda random, but this might help- what kinda deodorant do you use? It might not mean anything, but when I kept using a certain brand of anti-perspirant, I would get one of those lumps every now and then. They hurt, too! But eventually, they went away.
Perhaps you have an inflamed/ swollen mammary gland. It too should go away soon!
You can also get lumps from your period. I googled it a long time ago (seriously I was just as panicked lol) and it is caused by extra fluids.
Have you been jabbed in the breast by an elbow or something? Sometimes fat cells in breasts will die and cause temporary lumps. This one happened to me last September! I was at a lake with a bunch of people from school and I had just dove underwater off a floating/ chained dock, and the boys (duh) were rocking it, so when I tried to get back on, it slammed strait back into my chest! I had a HUGE bruise and lump for a while (and most likely not just from the skin swelling, but the fat cells died, to).
Listen, Blue, don't sweat it! Talk to your mum, as it is good to let her know, and she can help you figure out for sure what it is! Best of luck :)