How Can Irregular Periods With Intermittent Mild Bleeding Be Treated?

hi i am santosh, i have query regarding my wife ,my wife is having irregular period cycle, last month it got delayed about 15 days as scheduled, but in this month it also got delayed again for about 15 days, but this time she is having very mild bleeding, not normally as she was expectin, even we did both month pregnecy test through device, that result came negative, Please help me in this case what could be reason ?