Ecotopic pregnancy?

Christina • 20. Atlanta.05/23/14❤❤❤ soon to be married💑
I made a forum similar to this yestersay but still have questions.. I went to the hospital yesterday due to awful cramps in the abdominals and lower stomach and some symptoms similar to pregnancy and everything was ruled out but an ecotopic pregnancy or an ovarian cyst, as far as I've been told. They did a urine pregnancy test and it came back negative yet she still thinks I have an ecotopic pregnancy?? Why wouldn't they do a blood test? I haven't had a missed period just yet so I'm questioning the test. I have an ultrasound on Thursday w/ a gyno but how can they detect a tubal baby when I would only be 2-3 weeks along?It is frustrating and confusing me lol im also nervous..thanks for any feed back! I'm worried they will not find what's wrong with me.