12 days late for AF!!!????

Jessica
I am 12 days late for AF, I know I ovulated because I used opk. I have been slightly gassy more belching, lightheaded, and a tad bit of insomnia. Every test I've taken has been a BFN, and I have taken like five tests including a blood test a day before my period was expected. I need to know if anyone here knows can you be pregnant 6 weeks along or so and still get a negative test ?