Advice please?! Slightly TMI

I always get my period on time except for last month it was practically 3 weeks late. I was supposed to get it today, and instead I am feeling more fatigue then I have in months and my abdominal pain is so extreme it spreads towards my back. 
In addition to this, I haven't been able to use the bathroom(#2) in three days. Which isn't normal for me especially since my gallbladder has been removed over a year ago, and I make sure to have my daily intake of fiber. And now, as I finally was able to go, my pain became even more intense to where I cannot sit, stand, or lay down without it calming down. I've tried pepto, ibuprofen, midol, absolutely anything for it to ease...nothing...