What Causes Scanty Menstrual Period And Stomach Cramps?

hi.i am married for 7 months now and i am trying to conceive.i am not on any birth control pills. Usually my periods is a 25 days cycle but this month it started on the 29th day.I first thought that i was pregnant as my breats and nipples were swollen and sore.I wanted to wait for some more time before doing the HPT. But my periods came on the 29th day and is very scanty accompanied by cramps. Today is my 6th day and the flow is less.My periods last for 3-4 days at the max and i have regular periods. I am worried because it is scanty and it is the 6th day and i have stomach cramps and lot of gas formation.Please advise