After some consideration and Googling yesterday, I decided that watching a lump to see if it got worse went against everything I learned from infertility, which is, in short, that you should deal with stuff sooner rather than later. I may be wrong, but what I tell people is that no one ever regretted going to the RE now instead of in six months. I mean, hey, if you go to the RE and then get knocked up on your own, you can be one of those annoying people who tells everyone else to just relax.
And Dr. Google shared a few insights with me. One, 70-80% of lumps found during pregnancy are NOT cancerous. Two, you can treat breast cancer during pregnancy without harming the fetus (under most conditions). Three, women with breast cancer in pregnancy do as well as those who are not pregnant -- for the same stage of cancer. But, four, cancers are often detected later in pregnancy because people delay and because they're hard to find. And since, five, you can get a mammogram in pregnancy, I called the office back and left a message that I want an ultrasound and/or mammogram. Ideally, they'll just find a fluid-filled lump on ultrasound. But if not, I could at least get going on anything else that needs doing.
Update: The first appointment for a breast ultrasound is 8/19, so I'll have to stew for a couple of weeks.