Can someone PLEASE answer!

So okay you guys I'm really wondering what's going on, my cycles have been on the str8 n narrow for at least a few months now when all of a sudden magically this month nothing my period was due on the 16th of this month like clock work it would come, well nothing so I wait to test at least 2 days n all u got was a bfn, now today I'm on like my 4 day I'm not sure if I should test again or not, when I first noticed my period was messed all I had were sore nipples and the occasional heartburn or felt like food was sitting in my chest, so that's what made me test, but now I don't feel really much of anything, I'm not sure if u ovulated late or maybe just maybe af is on her way but either way I'm 4 days late, does anyone have any advice at this moment please oh please can someone tell me what maybe going on. I'm very unsure right now