Hello,
Thank you for your query at DoctorSpring.com
Yes it is normal for one breast to feel more sore than the other sporadically, but not always.
I don't quite agree that it may feel assymetrical and the fact that it's normal.
There are certain factors which points towards mastitis such as the cheesy scent, crusty discharge, and slightly lumpier.
There are various possibilities such as fibrocystic breast ( cyclical and hormonal ), mastitis, intraductal infection, e.t.c
I will suggest you get an Ultrasound of the breast, and that will give a much clearer picture. If there are evidences of infection, or if there is a fibroadenoma, appropriate treatment can be started before it gets too big. Fibroadenoma is a benign swelling, which occurs because of hormonal disturbances, and in initial atages can be medically managed.
Hence the prudent choice here would be to get an ultrasound of your left breast and follow up the reports with a general surgeon.
You can also upload the reports here when you have them.
Regards.