Baby making..

Hi there. My fiancee and I have been trying since January, lately ive had morning sickness, nauseas all the time, heat flashes, exc, exc. My last period ended Febuary 23rd (lasts from the 20th-23rd)  ive had negative results everytime i take a test..i went to the doctors and both the blood test and urine sample came back negative, they told me to come back in a month if i still dont have my period, could i be pregnant? If not what could be wrong with me..?