Why do I have to wait for my sonogram results?

My LMP was on Nov. 21st. It is now February and nothing. I always know when my period is coming due to certain symptoms and I haven't had any indication that it's even on its way. I took 3 Dollar Store pregnancy test 3 weeks ago and all came back negative. Today I went to the doctor to have a sonogram done (the sonogram tech only comes once a week with the portable machine) and I asked him if I was pregnant and he did not answer yes or no. However my doctor told me to come back in a week for my results. Shouldn't the tech have told me then and there? Why do I have to wait?