Why is there always a 'but'?

So I had my OB appointment today.  I liked the doctor, though the digs were a step down from the deluxe hospital clinics I used to frequent.  She did an ultrasound and said that the baby looked good -- and VERY active -- and the SCH looks as if it's absorbing.  She didn't measure it this time, but it did look more opaque and less black than before, so I saw what she meant.  They'll measure it for real at my big u/s at 18-20 weeks.  I then have the option of getting it ultrasounded at every appointment or just assuming it's all going fine.  Which do you think I'll choose?

BUT!  She found a lump in my breast.  Now, I had a breast exam in late June by my old OB, and I had a mammogram in February.  Neither of these facts made this OB say, "Oh, no problem."  We're to watch it.  Maybe I should have demanded a u/s right then.  I'm going to consult Dr. Google and then decide what to do next.