Pain in lower left abdomen, menstrual floodgates opened

I have pain in my lower left abdomen. It started 3 days ago, on Thursday. On Wednesday, in the middle of the day, my underwear filled with blood within a matter of 30 minutes. Enough blood that it soaked through my clothes and into my car seat. I assumed my period started, a few days early. Typically, day 1 of menstruating is light, and day 2 is when the floodgates open. Wednesday's volume resembled day 2 of my normal cycle. Then, on Thursday, I had no blood, however the pain started in my abdomen. The pain resembled severe gas pains, and I wrote it off as such. On Friday, my menstrual floodgates opened again and are still wide open. I attempted to work out tonight, although I've still had the lower abdomen pain, but much more subdued. However, when I did a sit-up, it felt like something popped in my abdomen, and the pain is leaning towards severe. Any thoughts on what's going on?