I Have Irregular Periods ,I Can Go Months Without It

I have irregular periods ,I can go months without it , and when I do get it it's the normal 5-7 days. Well this time ,I started my period on September 8th and I'm still bleeding and it's September 26 . I have lower back pains and some cramping ,I got a negative on a pregnancy test . Today I have like little stretchy things of dark I blood . Can an experienced doctor help me figure out what it is ?