I think I may be 4 weeks pregnant....but.........?

I think I may be just starting 4 weeks of pregnancy I had a couple days before my ov, on my ov and a bunch of times after my ov and my doctor told me that I have a good chance of being pregnant because I just got off of birth control but my doctor said I shouldn't take a test until 5 or 6 weeks of pregnancy well my grandma thinks i'm lying so she said I have to go to the doctor tomarrow to take a test and if its negitive I can't see my boyfriend anymore and at barely the 4th week it should come up negitive...I told my grandma that and she said its just an excuse, so is there a chance at all that the test I take tomarrow will come up positive if I am pregnant? What about if I take a blood test?