Negative HPT & blood test but still no AF

I am healthy & early 20's and my husband and I have been TTC for 4 months. AF is always a regular 28-30 day cycle for me.. But right now I am 9 days late. All tests came back negative but I have no sign of AF coming. I am not that stressed nor have I changed anything (meds, diet, weight, etc) any chance I could really be pregnant/what could be wrong here?