Anyone else had a lump post mastectomy for phyllodes?

Well, I'm six months out from my bilateral mastectomy and have booked in for my lat dorsi reconstruction after much deliberation and soul searching. Unfortunately I've just both seen and felt a lump under the skin. At first I though it was just my rib, as there is only literally skin and bone there, but on feeing it it feels more like a large insect bite...but it isn't.....sitting on a rib. I've also noted new swelling which looks like seroma swelling, same side, but in the axilla region. I'm away on our 20the Wedding Anniversary trip on Wednesday and working twelve hour days from now until then, so no time for any investigation before I go, and refuse to ruin another holiday because of this. Reasoning that even a malignant phyllodes can wait two weeks without adverse impact, and very unlikely to be much. Still wanted to know if anyone else has had this or a similar experience? Will probably turn out to be nothing, but if anyone has any comments (other than cancel your holiday), please get in touch.