Missed period 39 days sense last cycle.... negative pregnancy test

6 months and three weeks ago our first baby was born. I started cycling after 3 months on average every 24 days.... I am now 39 days out sense my last period. I have taken 4 pregnancy test 3 days apart. All negative reads. I guess I have a few questions.... one is this normal? And two could I be pregnant? I have been overly weepy. Which is not the norm for me. I should also add my daughter has just lost intrest in nursing. Maybe this an effect?! Hmmm.... any help, advice or opions would be greatly appreciated. Feeling confused.