Late period

My cycles is normally about 40 days. But that’s been for the past two months or so, I went off the pill about 6 months ago because it wasn’t working for me, I’ve been on numerous brands and nothing worked. Currently I am 7 days later than I have been for the past two months, but for the whole 7 days and a bit before I have had all the symptoms of getting my period, cramping, tender breasts, bloating and acne. There is little to no possibility that I am pregnant. What is happening? Is it maybe that I am stressed? I’m a year 12 student.