lump under breast

Hello ladies
I have recently had a re- excision after WLE and full axullary clearance. 3 out of 18 positive nodes. Got a nice seroma .
I have recently felt a lump under my breast, really on my rib just to the right of my right nipple line . Its painful if a press hard. About the size of a flattened marble. Anyone else had something similar ? I’m wondering if this is a lymph node that was missed or something to do with the seroma , which is slow to drain.
Had a CT scan 2 months ago which showed no activity in that area. The CT scan did show a 4mm inter- plural noudle in my lung. Not sure its cancer have to have another scan in a month. I’m hoping it will be an old infection scar. However I’m getting very despondant. I was diagnosed in feb and still trying to get the surgery right. I’ve been told I’m going to get herceptin , But when is anyone’s guess.
Getting the results of the re- excision wed 16th - margins were showing residule DCIS - if it’s not clear they will ‘talk to me about mx.’ I feel - just get on with the chemo / herceptin and do mx later.
I’m at my witts end worrying about this almost constantly. I need the strength to say this to the team without being bambuzzled by the surgeon. With this lastest developement the picture is even more confusing .
I’m 59 and had breast cancer two years ago on the other side which was delt with by lumpectomy ,node clearance and rads . No chemo as there was only a trace in the SLN.
Any advice would be most welcome.
Helen