Need some help!!!!

Okay so 2 weeks ago I took two pregnancy test and they came out positive, I then took another one a couple days later and ever since then they have came out negative. I still haven't started a period, havent hade any cramping nothing. I went to the doctor and they did a test and it came out negative. He said that it's possible that I am pregnant just my levels arnt high enough to produce a positive. Witch I don't understand cause I already got two positives. He said to give it two weeks and see if I start or anything. I went to just my family doctor. Do you think I'm better off going to my ob?