What's wrong with me??!

So I'm now 17 dpo af is NOT here. my cycle is normally 28 days and many pregnacy tests are negative even clear blue digital. What's going on with me? Even a nurse at my Ob office said if I were pregnant a test would be positive already. Any ideas as to what's could be going on with me? Should I still have hope of pregnancy? Please let me know. Any advice is much appreciated.