You COULD be skipping periods due to stress, bad diet, lack of exercise, or exhaustion.
However, if you think you're pregnant you probably are - I am a believer in women knowing their bodies better than any doctor. Have you had any other signs of early pregnancy?
Not to refute the dr, but I've never had a home pregnancy test work until 12 weeks. With my last pregnancy, I even had two blood tests - at 8 and 10 weeks respectively - prior to having XRays and both returned negative. Some women just don't have enough progesterone until later into the pregnancy to get a positive positive and end up with several false negatives first. I am said woman. You may be also - was that true of your previous pregnancy(ies)?
Also, keep in mind that it takes awhile to start ovulating typically after discontinuing birth control - and you WANT to be pregnant, probably pretty badly, so your body could be playing tricks on you.
I'd discontinue any medications that may adversely affect a pregnancy immediately and give it a month or two. Wait until you think you're ten or twelve weeks and try another test if you haven't menstruated by that point. If you receive a negative, definitely make an appt with your regular OB/GYN.
GOOD LUCK!