You seem to be suffering from a temporary disturbance of the HPO axis; causes could be many; in your instance, the most likely ones are the change of weight, life style and added medication ( though the medication itself does not cause cycle disturbance). Yet, if you are concerned, you may contact your healthcare provider for a general exam and investigations like a hormonal
profile, sonogram of the pelvic organs etc. Once you are properly examined, the cause can be elicited and management is possible. Take care.