Spotting.....wtf????

Before I had my period I took a pregnancy test...it came out negative. 
Then I got my period & it only lasted for 2 days. Which I found odd because that has NEVER happened before. My period ALWAYS stayed on for 4 days ever since I started getting my period. 
2 days later I started spotting but I didn't think anything of it but now I'm spotting again 4 days later & I've been getting cramps since yesterday (first time I've EVER had to deal w/Cramps) & those cramps were terrible. 
I have not been stressing out about ANYTHING & nothing has changed in my eating habits either (just in case somebody says these things). 
Has this ever happened to anyone?