Mother had lobular breast ca at 54. I'm 27, had an breast ultrasound which came back normal but radiologist said they can't see lobular on u/s? Is this true? Am I at increased risk for lobular ca?

Harder to see. Lobular carcinoma can be detected on mammogram or ultrasound, but it can be harder to detect than the more common ductal carcinoma. Lobular carcinoma is best detected with an MRI but I do not suggest this at your age (or an ultrasound for that matter) unless you have signs or symptoms that warrant it.
That may be true. depending what type of "lobular" the radiologist was referring to. Lobular carcinoma in situ(LCIS) is virtually impossible to detect on ultrasound. Invasive lobular carcinoma can be detected on ultrasound, but not always. Lobular carcinoma is more difficult to detect on US/mammo than Ductal carcinoma because of its propensity to extend along existing tissue planes rather than form true masses.
Yes. You are at an increased risk for breast cancer which may be lobular or other types of breast ca due to your family history. Lobular cancers may be harder to be identified on mammogram as well as ultrasound. But if your ultrasound was negative do not imply that you may have lobular cancer. Stay proactive in your breast care with regular self exams, clinical breast exam and breast imaging as needed.
Yes. You are at increased risk for any type of breast cancer. Try this risk assessment tool, http://www.Cancer.Gov/bcrisktool/default.Aspx , then speak to your doctor about your choices of early screening such as abus, mri, and beginning mammogram before age 40y.
Iobular breast ca. Lobular breast cancer can sometimes be missed on mammograms but the new digital mammograms have a higher diagnostic yield. Mri breast can be useful in someone who have lobular cancer and initially missed on mammogram or us. It is also indicated for brca positive cancers and for women with dense breasts. I don't think that you are at increased risk for lobular cancer.