Sorry to hear about your problem. This is a common problem after lactation
. It is good that you are regularly checking your breasts for lumps.
To relieve this pain, you should wear a well supported bra (sports bra's are helpful). In addition to that avoid caffeine (coffee/ tea). If the pain still persists you can try Vit E capsules. With these measures the pain would go down within a month or so.
Hope you get well soon.