Period 3 days late but BFN on the first day?

My period was due on the 17th and it’s currently the 20th. I took a test on the 17th, and BFN 😔 but my period still hasn’t come! I’m on cycle day 30 and I’m never usually this long... I’m afraid to test in case of another BFN.. and if I’m not pregnant, then my cycles are all of a sudden irregular and I’ll wanna go to the doctor to figure out if there’s something wrong! After all, I’ve never had a pap in my life. Lol. Do you think I should test again tomorrow morning??