Late period but negative pregnancy tests

Hi, I'm a newly married wife of 9 months i usually have irregular periods with my cycles ranging from 25 to 40 days. 
This time around, I'm on my 43rd day and for some reason i'm feeling that this is different.. Not sure if it's my imagination, so I had a pregnancy test on day 32 and 40 and they all came out negative... 
Is there a chance that those could be false negatives, or could it be just a particularly late period?