advice needed!

So I started a birth control about two months ago.. Simpesse. It’s a 3 month dosage with the placebo pills at the end of the third month. Everything was fine until the second month.. and now i’ve been having brown discharge & some small clots for almost 3 weeks? I’ve never experienced this with any other birth control and i don’t know if it’s normal. i’m having slight cramping too. I took a pregnancy test about two weeks ago bc i missed a couple pills during the first month.. but i’ve been taking it right for over a month and i’ve been having the brown discharge?? the pregnancy test was negative but it’s kind of startling me. It’s still going on. it’s not enough to fill a tampon but it’s enough. does anyone have any advice on what to do/what it is?