Hi, I just read your post, and i may have an answer for you. My friend here had missed 2 periods, we did a test and it came up positive. It was ectopic, we didn't know until she had an ultrasound though.
Take a test again with your ob/gyn and they can help you figure it out. There are things such as false positives and negatives.
Hope you get relief and answers
love ya bunches
Linda