Changed Period

I used to have a 4 day period with a cycle length average of around 32. I was never completely regular but it was mostly 29-35 days. This summer my periods changed completely and now they last about 2 days, I don't have cramps or sore breasts anymore and the cycle is very irregular : 29, 27, 23, 26 days. I've also gone down a cup size. 
​I did start running a lot more again and am up to 30-40 mile weeks now but I've always been very active. 
​Should j be concerned?