Period late, negative tests

I noticed my period was late by a couple days and I was extremely excited to take a pregnancy test, and it came back negative. I waited a few days and took another test, negative. A few days later I bought another box, both tests negative. (I know I’m spending too much on tests, lol!) I am CD 38 now, still no period. My cycles are always 28-29 days. Do you think it is worth going in for a blood test?