I remember my last period started on 16th June,...

Treatment for delayed period:
Well, it should be noted that it could be pregnancy as it's one of the commonest causes of delayed period. So it's recommended to do a pregnancy test at the beginning, and if the test result is negative, then further assessment by Gyne & Obs doctor has to be done.
If the problem results from hormonal disturbances, then OCP might be prescribed. Furthermore, It is advised to take enough rest and sleep, follow a good diet rich in vitamins and minerals, and avoid stress as much as you can.

Diagnosis:
First of all, pregnancy test should be done to exclude pregnancy. Then an examination by a doctor should be done. Further investigations can also be done such as complete blood test for infection, TSH, T3, T4 to rule thyroid problems, prolactin, FSH and LH hormones, to detect hormonal disorders. Pelvic ultrasound can also be performed to rule out PCS.

Causes of delayed period:

• Pregnancy
• Stress
• Polycystic ovaries
• Malnutrition
• Thyroid disorders
• Using contraceptive methods 
• Hormonal disorders such as elevated prolactin
• Others

Recommendation:
It's recommended to do a pregnancy test.