2 days no AF and still testing negative?!

Ally
I have never once in my entire life been late on my period. Granted, I did have an IUD for 5 years with no period at all...but after I took it out I immediately got back on track with regular periods. Like to the day. Exactly 28 day cycles. The first time we TTC, all of a sudden I'm late?! Is it just coincidence?! I have tried 3 different brands of tests. Tested day before AF was due, tested day of, and day after. All negative. This is so frustrating...I just wish I could know if I am or not! Any advise?!