Pregnancy or due to just stopping BC 1 month ago?

DH and I are TTC our 1st. I stopped taking BC (pill) on July 4th. AF was very irregular before I started BC (about 8 years ago). AF was like clock work while on BC. This past Monday at 3AM I had a BFN and Monday evening AF came... But it has only been spotting and AF is usually pretty heavy. Could it be because I may be pregnant or could it be because this is my first cycle off BC? When should I test again?