Suggest Suitable Treatment For Breast Cancer

Hello there. I am a 55 yr. old female that had breast cancer 3 yrs. ago. Went thru Lumpectomy followed 1 week later with removal of 1 lymph node then radiation. I have now developed a pocket of fluid ( white, sticky mixed with blood and clear fluid), in the area where they placed the dye to do the lymph node removal. This area has been getting larger and harder since then. I talked to my Oncologist about 3 months ago and have had a recent Mammogram that has come back normal Lab tests have been done on the fluid which shows no infection but I was placed on 2 antibiotics ( 1 for Staph and 1 for bacteria). I have seen my Primary Doctor and she has suggested that I see my Oncologist. My question is Why after 3 years this is happening and what could be wrong/