I Am 28 Years Old, Female, Married With Two Kids..no

i am 28 years old, female, married with two kids..no abortion before. no surgical history before.no medical history before.my height 155cm. my weight is about 69kg. the c/o that is i had my last period 16/9/2015.it is a prolonged menses up until 1 month.exactly stop on 17/10/2015. then until now i still havent had my menses...since it stop on 17/10/2015. currently i do the test of upt...second line look lightly pink appear..but i still curious whether i pregnant or not..after 2 day..i check with the otherdevice..then..it is negatrive result...before this..on 15/9/2015..i had done scan..and the doctor had detect me having cyst about 6x6...but untul now i didnt followup my cyst...recently i having my lower back pain and mildly lower abdominal cramping like having pms..but still not having menses..what should i do?