m found, still feeding-HELP!!?

I have a m in my right that is not getting smaller. I am now on my third antibiotic and am scheduled for an ultrasound tomorrow of the lump. The hospital refuses to do a mammogram if I am still feeding. But-what if the m is something significant? I cannot just abruptly wean my son as he has a severe milk and soy protein allergy which prohibits him from taking ANY formulas. Is there any place that will do this procedure if you are lactating, and should I be worried about cancer? I am 32, no family history of any cancer, and otherwise very healthy. I might mention for about 3 months now though, my right is about 3 times the size of my left. I thought it was due to nursing schedules with the baby, but it is a big difference. (like a C cup on the left and a DDD on the right, and the m is in the right side!) Thanks for all and any help! God Bless~Taunya