I think that if I were in your situation I would *try* not to do an urine pregnancy test until my period was actually late. On the other hand, if the GP can send you in for a blood test tomorrow then you might as well have that done now since its results are a lot more reliable this early in pregnancy than those of an urine test...
The annoying thing about most early pregnancy symptoms is that they are so similar to end of cycle & onset of period symptoms... I suppose breast discomfort is one of these ambiguities. I would mention it to my GP but I tend to make my docs work hard for their $$$ and --as a matter of principle if nothing else-- I like to take FULL advantage of m.d. visits and make it a point not to end the appointment until ALL my concerns have been thoroughly addressed

. But, I've also never been squeamish about physical examinations since I figure docs are pretty desensitized to the sight of human anatomy so I don't problematize the inherent awkwardness of those few minutes for very long --if at all.
One last thing: if you do end up following through with IVF I promise you that it's actually not that scary. At least in my experience, IVF was more of a hassle than anything else but I actually liked the feeling that I could proactively DO something to increase my chances of having babies. It's true I only did it once for the equivalent of one cycle and I figured I could do just about anything (shots included) for a month. I'm looking at my twins now (literally because they are sleeping in their co-sleepers next to me) and they were so ridiculously worth every shot. Without IVF I wouldn't have them and would still be trying to get pregnant and THAT's way more terrifying to me than anything the IVF entailed!
But good luck tomorrow and if need be at your appointment with the RE. I know it's nerve-wracking...