I got my period two days

I got my period for today’s then it stop this period was the weirdest I am 5 days regular 28 day cycle with heavy bleeding and clots this one was just two days and nothing I got a very fainted positive then a week later I tested again and got a negative I been having cramps and a lot of abdominal pain with lower back pain and crazy craving but I went to the emergency room they did a urine and a blood both came out negative . I ask for a ultrasound and she told me no follow up with your doctor your not pregnant but I had the same thing happen to me 6 years ago I had my daughter premature at 26 weeks due to not knowing and everything coming out negative. Help what do you guys think?