Period Trouble

Last month, my period delayed for about 3 days, I freaked out and went to buy a pt strip but I wasn't pregnant. I had cramps and my nipples hurt but my period wasn't coming. At last when it did, it was dark brown in colour and didn't flow very well. It ended in about 2 days when my normal flow is 4 days. Same thing is happening this month. 2 days delay, and my nipples have been hurting for a few days now. Was having slight cramps but this evening, the cramps were intense and when I went to check, the blood is same as last month, dark brown. Now I'm freaking out Ladies what do you think it is? Any of you experience something like this?