Ugh help

Alright so I've called my doctor multiple times. And have not gotten a call back yet. And I can't find my answer on Google. So I'm coming here. I've been on the pill for a while. Years. Well lately (past 3 weeks atleast) I keep getting this light brown or like dark red clot lookin things when I wipe. They're like stringy? I get my period every three months. I haven't gotten mine yet because I've just been taking the pill. I haven't given myself it yet. But this has been going on for about three weeks. It won't stop. It's not like blood. As if I'm bleeding. And it doesn't go in my underwear. It's just when I wipe. But I want it to stop. I took a pregnancy test just in case because I get paranoid about everything. It was negative. So why is this happening??