When can I test?

My period was originally due last week but never came. I’ve been testing and all have been negative. Yesterday I had a very very scant brown spotting on my underwear. According to glow, as my period gets later and later, it looks like I may have ovulated on the day we bd’d. Is there any chance that was implantation? If so, when should I see a positive? I’m sick of wasting money so I don’t want to test everyday or unnecessarily.