Implantation bleeding? Or super short light period?

I stopped taking the pill about three months ago. It took 43 days for my period to return the first month. This time my period came after 33 days. BUT it was extremely extremely light and only lasted for two days. I took a pregnancy test a few days before the spotting and got a BFN. When should I test again? I don't really know when to expect my period as my body is still normalizing itself. I don't want to just keep testing haphazardly until I get a BFP or a real period (my usual is like 6-7 days). I feel like I'm single handedly supporting the testing industry with my purchases over the years! Any insights?