Understanding Mammograms and Ultrasounds for Breast Health

Question
Appox 1/06 I felt a lump on my R breast, went to OBGYN 1/07, he felt 2 others on R and none on L.  Mammo showed small microcalcifications on both L and R but more on R.  US shows NONE on R and 3 on L. (Simple cyst)  Could the tech doing the US have missed something on the R???? I am really confused, I can still feel the lump and one other that has been on the right breast for the past year. Could the lumps be something that won't show up on an US?

Thank You

Answer
It IS possible that the lump does not show up on ultrasound. 2 things should be done! 1. A breast MRI of both breasts should be done and 2 (most important) a needle biopsy (easiest and quickest as a thin needle biopsy) should be done of your lump ASAP! Please do keep me posted!