spotting instead of period? same exact day?

Hi so this may be a little ridiculous and just me and crazy anxiety but I thought I'd post anyway.

I'm about 7 months in on Aubra BC and I've never missed a day - late like maybe twice? But have always used condoms. The last time I had sex was in July but suddenly every period after then has been really light spotting to barely any blood at all? It happens right when my period is supposed to come but I thought my period would be lighter 3 months in on BC not seven? I've also been getting nauseous and gaining weight even though no dietary changes. I took two tests in July but got negatives - not sure if they could be false or? Just wondering if anyone else has had a similar problem.