HPT's these days are pretty accurate, especially this far overdue. Honestly, it's not possible for your levels to be so low as to not get a positive unless you are not using the test properly (which is very easy to do). That is the number one reason for false negatives and it happens a lot. You also would not need to use first morning urine at this stage.
See your Dr. for bloodwork to know for certain. I wish you well.
it's true if you have really lower levels or low rising levels you might only get a positive on a blood test. most urine tests will show a positive at 25 mil HCG however I have had friends who just never got a positive on a urine test they had to do a blood test.
If you still have gotten your period I would just call your doctor for a blood test , it will at least put your mind at ease and have you not stress out
The best way to find out is a blood test, but maybe try taking another HPT using your first peepee of the morning, when hcg is more concentrated.