TTC - chances of positive?

So have been trying for baby #1 for 3 years now. I usually ovulate early (around days 10-12). This month I didn’t test but had all the usual symptoms that I get when I’m ovulating at around the same time frame.

On day 16/17 I had some light bleeding (brown/ light pink in colour) - I’ve never had this before. Could this have been implantation bleeding?

I tested today (day 21) but BFN. Is there any chance that I could still be pregnant even if the test is negative (it was a cheap test not an early response one)? If it was implantation bleeding, surely it would be showing positive by now?