13 DPO, AF due today... VVFN

Hi ladies I’m looking for some advice on Sunday I decided to take a test and it was a vvfn and continued to test with cheap tests up until this morning. The line darkness hasn’t changed. I tried a digital cb test yesterday and it said not pregnant but I’m thinking I just have a low level of hcg. Last night out of nowhere I got a pounding headache and random wave of nausea and couldn’t stop throwing up. Is this all coincidence? I’ll retest in a couple more days to see if it darkens but just wanted to get opinions.