I need advice

So I am on the pill and my partner and I never use condoms, and he finishes inside me every time. We just rely on the pill. Since starting birth control about two years ago, my period has been irregular sometimes not showing up for months. The last few months I've been having a somewhat regular period, comes at the same time each month and I bleed very lightly for about a day. This month though my period never showed, I'm two weeks late. I took two tests and they both were negative. Today I was having light cramping and went to the bathroom and sure enough I was bleeding extremely light just enough to see it when I wiped. The cramps were on and off all day but they were bad. Now I'm only bleeding dark red blood thats only in the form of clots. This is extremely abnormal for me and I was just wondering if I should be concerned.