TMI but idk what’s wrong with me

so my period this month was 3 days late which is not very unusual. but i’m barely bleeding, i’m spotting at best. the blood is dark brown which i assumed was old blood but in the past 3 days i’ve had 3 very big chunks come out. they’re black and they’re not the same consistency as blood clots. it’s stringy and very very thick. the chunks are big and today when one came out i got a terrible stomach ache right before it came out and then immediately felt better right after. i’ve also had pms worse than ever before over the past 2 weeks. i’ve been exhausted and so irritable/emotional which isn’t normal for me. any idea what might be going on?