it is hard to say about the lumb there or the pain. i was on the IUD for about 13 month , just had it taking out about a week agou.
i must say i had severe breast pain in both of theme, starting about 6-8 month agou and then it keept on coming and going. now i dotn have big onces at all but the started to get bigger , wich i thought was nice but the pain came allong with that. hell i could not even touch theme and i have a 9 year old little boy who loves to cuddel with me , plus i drive a big rig so when i came in after beeng on the road for 2-3 weeks and he wanted to cuddel with me and hug me and just lock on to me, i always had to make sure he wasent near theme becourse the hurt so much. getting out of bed in the morning , i had to hold theme so the would not drop down and hurt when the dropt, and like i sayed, iam not a big girl at all.its is hard to say for me about the lumb becourse i didnt have one at all, just the pain, man the pain. but i had my IUD out 1 week agou today the 19th of july, and i never feelt better. my breast dont hurt at all no more and all the other side ffect went away. i was spotting for a couple of dayes and then sunday or last saterday i was bleeding with clots, but more like a heavy periode and now it is gone.the removes was a breeze. and i had no cramps , nothing.
but anyways, i think if i was in your shoues, i would keep the iud out for a while , maybe a month or so mabe even 2 month and see how it goes with the breastpain, if it goes away and stayes away then great, you know it was from the IUD, but if it sticks around then you know it wasent the IUD.
good luck and keep us posted .
By the way, be ready that your doc, will tell you that there is no way in hell it could be from the IUD.