Estrogen levels in the body are one of the parameters used for estimating the function of the axis hypothalamus – pituitary gland - ovaries. Low estrogen levels can be due to hypogonadism, which can be primary (ovarian disorder), secondary (pituitary disorder) or tertian (hypothalamic disorder).

It is not clear from your question if you are ovulating, or not. Menstrual cycles without ovulation are usually irregular. Further, your symptoms (feeling sick and lower abdominal pains) are not specific enough and can be found in many conditions including pre-menstrual syndrome PMS. The pre-existing conditions you mention (migraine, depression and anxiety) can also cause or at least contribute to the condition.

There is no data currently available to confirm that your migraine medication (mersyndol forte) can cause low estrogen levels. Dry mouth, ataxia, urinary retention, and drowsiness are mentioned as side effects of this medicine.

Several diagnostic procedures should be performed to identify the reason for low estrogen levels, including: hormonal analyses (FSH, LH, prolactin, testosterone, thyroxin...), an ultrasound scan of the ovaries, a Pap-test, etc. You can consult an endocrinologist and a gynaecologist for further information about your condition and to schedule follow up diagnostics.