Implantation of the fertilised ovum into the rich endometrial lining of the uterus often causes spotting. Typically, this occurs a few hours to a few days after implantation, which occurs up to three to five days after ovulation.

Pregnancy tests turn positive around the time the period would be due, but in your case, it is hard to tell when that would be. I would count two weeks from the spotting and do the test then; if it is negative, wait one week and repeat it. If it is positive, talk to your GP.

This is not terribly unusual after the cessation of birth control pills, especially if you were a bit irregular before starting them.

I wish you happy news.