NO - you are not overreacting at all.
It is very likely you could still be pregnant - it does happen that people to spot and cramp for the first 2 months of pregnancies. It's likely that you could have an ectopic pregnancy. Whether or not either of these is true, the nurse should have just said, "Why don't we set you up for an ultrasound to try and see what's going on, and we can go from there."
I would actually suggest going to a different doctor. I've had good luck with Brillhart OB/GYN, and David McLaughlin in Noblesville (www.familyjoy.net).
Keep in mind that some pregnancy tests aren't that good. I've heard of several who took EPT tests, showing they weren't pregnant, but took a First Response pregnancy test, and it showed pregnant. The best way to find out is to have a blood test and an ultrasound.
Whatever happens, let the doctor know about the conversation with the nurse.
Good luck!