Late AF

So I’m going on day 26 of my period being late, I have taken at least 3-4 At home pregnancy test which were all negative. I did one at my drs office when I was exactly 2 week late and that was negative as well. He can’t give me any explanation on why it’s late, He just said to come back in 2-3 weeks for another test. Any advice or any insight to a situation similar would definitely help me figure out what’s going on!