Severe cramping and sharp pains during early pregnancy

Did anybody have severe cramping and on and off sharp pains in the stomach and in back? I'm three weeks pregnant exprence all this and I went to er and they did a ultrasound said they didn't see anything in my tubes as of now or really couldn't see anything all! My levels are 130 and told me to find a ObGYN and be tested again Wednesday and see if they double! Is this coming or does this sound like a miscarriage or a tubal