Advise please! 10 days late and negative tests!

My husband and I have been ttc for about 1 year now and my periods are ALWAYS regular. 26-29 days usually But this month I am 10 days late??!! I have not been stressed or change anything in my life to cause my period to be late but I've taken 4 tests and all are negative and with first morning pee. Has anybody ever had anything like this? I'm keeping calm because my husband gets so excited and I don't want to let him down 😞