I hate the pain of the mammagram so how painful is the breast ultrasound?

Not very painful. Unless you have an underlying problem such as an infection or trauma, an ultrasound of the breast should not be more painful than a light massage. A probe combined with a special gel is used to look at the tissues. A mammogram can be painful to some since the breast is pressed between the x-ray .
Painless, but... Breast ultrasound is essentially painless however it does not replace a mammogram. Mammograms are most useful for cancer screening, looking for a cancer before it is evident on exam. An ultrasound is a poor screening tool; it is most useful for helping to define if what we see on mammography warrants biopsy. As painful as a mammogram is for you, please get them yearly--they really do save lives.