I'm never regular but this time I was 3months late, all pregnant tests were negative, finally I got a very lite period, but still was regular length?

Didn't ovulate. You more than likely do not ovulate regularly. In order for a woman to have a regular menstrual period every 28 days (give or take a week), she needs to ovulate regularly, assuming the uterus, uterine cavity, and uterine lining (endometrium) are normal. In most women, treatment can be a simple as going on birth control pills, assuming that pregnancy is not desired. You should see your ob/gyn.