Mamogram

Has anyone had a mammogram and they found a mass but were unable to tell you what it was? They say they believe it's debri but can't explain how it would have got inside me. As well they say they believe it is benign but they are not sure. They want me to wait 6 months to have another mammogram to see if the mass hasn't changed but I feel very uneasy about doing this especially since I have had cervical cancer before and I have a autoimmune disease which lowers my immune system . Also today I received a letter explaining the same thing but now it also mentions some law about breast density has anyone heard of that? Any information would greatly appreciated thank you. 😕 🤔