Am i pregnant

Help. I am one week late pregnancy test negative I was suppose to get my period on the 7/20 I had mild cramping in my stomach and I was vomiting I ended up going to the er because I was so sick they took blood on 7/21 and negative it was.i usually get my periods from the 18- to the 20th ranging start date. Anyways they thought maybe I have ovarian cyst but that came back as I don t. I no longer have period cramps to often now my lower back hurts and I feel nauseated at times I have been getting heart burn lately my boobs are not sore. I have no new stressor s in my life nothing new. Just not getting my period. Me and my husband have been trying to Conceive For three years now with no luck my last test was done on 7/ 25 and was negative. So I don t know what to think now.