No period, negative test, yet...

courta77

Hi everyone.  So I haven't gotten my period since June 6.  I was due for it on July 6th (there are typically 28-30 days between my periods).  That date came and went with nothing.  On July 12, I took a Walgreens brand pregnancy test, and I took another one a few days later - both of which were inconclusive.  On the 17th I had a blood test done at my doctor's office.  The next day they called to say it was negative - no trace of the pregnancy hormone. 

Now,  17 days after my period was due, I'm spotting a little, but nothing to even wear a pad for - a pantyliner or nothing is doing fine.  My husband and I keep track of my ovulation and wear condoms when we're around that time, otherwise we don't use any other protection. I'm not under any particular stress or going through anything stressful (I'm a teacher with none of my own kids, so I'm just hanging out at the house for the summer).

One of my friends had a blood test from her doctor that was negative yet she was pregnant a few years ago.  Could that be the case here?  Any advice or experience with this sort of thing?