Pregnant with the Paragaurd IUD?

The past week I have been so nauseous, have bad back pain, light spotting a couple days, and light cramping. My period was on Sept 2nd. I had sex on the 5th and again a couple days later. Right when I was ovulating...but I have an IUD so who cares. Well now I'm getting these symptoms I had while pregnant with my son and this odd feeling that I am pregnant. Like I did with my son.. I just knew it. I think it's too early to take a test, but I need to know. I am worried about if my baby and I would be okay if I am pregnant. When should I take a test? Has this happened to anyone else?