late period, bfn

My period has been late by 5 days already. I'm on cycle day 35 and that's pretty odd for me. My periods aren't super regular, but they're never that late. I've been having mild cramping for a couple days. But prior to that I've had mostly all preg symptoms which made me take the test in the first place. I took one the day before my period was supposed to start and one the day of. Both came out neg. 5 days later now I took one this morning and still negative. Is it possible that my hcg levels aren't high enough yet? Or am I experiencing something else. I asked my bf and he said if I tested today it would definitely be able to detect. Help!!!! I really want to know if I am that way I can stop wondering ever single day if I have a small human inside of me waiting to develop. Thank you gals!!!