Period concern...

Sorry for the info but I've never had this happen to me. My periods are always short & light has been for 15 years. For the past 4 months I've been late on my period but my periods were normal. This month I was 3 weeks late & 3 days a lot I started spotting & I've been having lower back pain really bad. Today is was worse the lower back pain & the bleeding! Sorry TMI but it's way more than normal & my having really bad blood clots & the blood almost looks like I'm having a nose bleed & I've had to changed my tampon 13 times today! This is abnormal for myself. So I'm a lil concerned