Hallow Dear,
Since 15 days after the missed period, your pregnancy test is negative, you are not pregnant. If the delay in menses is due to hormonal disturbance or dysfunction of the reproductory system, you should get menses (withdrawal bleeding) about 4-7 days after discontinuing
Dydrogesterone. Have you stopped the tablets after 10 days? If not, please discontinue them now and you will get menses within 4-7 days.
If even after the discontinuation of the Dydrogesterone tablets you do not get menses, then you need to undergo further investigations for any other causative factors like
Thyroid dysfunction, ant intra-abdominal factor or intrauterine factor or otherwise. The first investigation I will suggest you to undergo
ultrasonography which will reveal lot of things like missed pregnancy, PCOS,
genital tuberculosis, etc. If no cause is detected, then you should get your blood examined for FSH, LH, Prolactin, Oestrogen and Progesterone and
Thyroid function tests (T3,T4,TSH). If they are normal you may undergo laparoscopy and hysteroscopy.
However, I feel after discontinuing Dydrogesterone tablets, you should get menses in due course.