What Causes Delay In Periods?

am facing delay in periods from last month. last month periods came me for 40th day. this month not yet came ,now its 51st day. i did my family planning by laproscopic ring insertion.now 1 and half year after family planning. i have 2 kids younger 2 1/2 years .i stoped feeding him by october last. first time am facing delay periods from last month.

am 30 years of age, weight 70.lstaying in saudiarabia