What Causes Delayed Periods After Taking Metformin?

i am having metformin 500mg since 1 and half months..for the first week dr prescribed 1tab each daily..after that start having it twice daily.after started metformin ma first periods got delayed up to 11dys .dr prescribed a hormonal tablet to get ma periods and got periods with normal flow and heavy pain.now itz the time for getting ma second periods on metformin ..didnt gt yet itz been 6dys late now..why this happens?i hav severe back pain ,breast tenderness,severe leg cramp,constipation ,feeling light sleepy this time.why it happens? (having levothyroxine 50mcg for 7mnths .diagnosed with pcos 7mnthsbefore ..i am married since one year and trying to concieve. i had periods everymonth before strarting metformin wid 3,4dys late or 3,4dys before)ma thyriod level is 0.5 now ..height 161cm,weight 60kg