New Lump on Mastectomy Scar

Hi there. I am new to these boards. Diagnosed in March of 2016 with stage 3, grade 2 ductal carcinoma. 12 weeks of AC/Taxol chemo, bilateral mastectomy, 30 rads. Currently on Tamoxifen and Palbociclib (clinical trial). I have not even been out of treatment for a year - finished radiation last Dec 30th - and now I have a small hard, round lump right on my mastectomy scar. I am going in for an ultrasound tomorrow morning and I am terrified. It seems to be getting bigger. During my mastectomy, I had 14 lymph nodes removed and 7 of those were still positive (after AC and Taxol). Everyone is praying for me, but that is somehow no comfort. Has anyone else had recurrence at the site of a mastectomy? Was it just localized or metastatic. I'm not sure I a strong enough just yet to do this all over again.