Period help?

So my period has been regular for about 5 months now. And they usually last 8 days. Well my last one in November was only 4 days long. And I usually don't pms but for about the past week I've had some bad cramps. And really bad back pain. And I've always felt bloated. I took test about 4 days ago and it was negative. Now Im starting to notice a thick creamy white discharge Thats been going on for three days. I just wanna know what's up.