What could have caused this?

So earlier today out of nowhere I got this really bad stomach ache (and I rarely get stomach aches). Then I felet the need to use the washroom, but where I was had no facilities, so I tried to hold it. My stomach ache got really really bad though and I really had to go, so I drove to a store to use their washroom. Sorry for the details, but.. when I had a bowel movement, I had to push pretty hard to get it out, and it really hurt my stomach to push. It was also really big and hurt coming out and there was a lot of it (like at least triple the usual). I felt a little better after that, so I started driving back to where I was originally, but then I had to go again? It hit me really suddenly and I like HAD to go, so I pulled over and went in the forest (gross i know but trust me i had no choice). This time it was diarrhea and there was A LOT of it.. anyway.. what could have caused this? I still have a stomach ache now and since then I've had another bowel movement, it was normal but also a large quantity.. where's it all coming from??