I've been trying to concieve for a while and im now 6 days late. Pregnancy tests are showing negative. I would always be on time. What could be wrong?

Maybe nothing. Menses can vary normally perhaps you did not ovulate that month so your period would not be on time check with gyn to be sure you are ovulating good luck.
Needs clarification. You have pregnancy tests done-which one-urine or blood test. Urine pregnancy test may not shown yet if hormone is low , but sreum pregnancy test should show already if you are pregnant.Otherwise stress or hormone imbalance including thyroid may affact your period.You need to get evaluate if this is a new symptomfor you.