You seem to be having secondary amenorrhea. Secondary amenorrhea is when a woman who has had normal menstrual cycles stops getting her monthly period for 3 or more months.
Common causes of secondary amenorrhea include stress and anxiety, depression, over exercising, sudden weight loss or gain (obesity), thyroid disorders and hormonal imbalance due to polycystic ovarian syndrome (PCOS).Smoking is also associated with secondary amenorrhea.
I’ll suggest you to consult a gynecologist and get it evaluated.
I hope it helps. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.