Hi I Will Get Periods Very Regularly Every Month A

Hi I will get periods very regularly every month a 5 day earlier,but this time I am delayed by 15 days
10 days doctor prescribed me regestrone 10 mg for 3 times 3days but still I miss my periods I am having mild cramps also. I am diabetic I am sterilized 4 yrs ago I am 35 yr old. I am taking thyroxin tablets daily.suggest me what do next.I have taken urine test it is negative