I am 24 years of age. My height is 5.5 and I weigh 55 due to the fact that I am 21 weeks pregnant. I have been experiencing terrible back aches, sleepless nites and and an excessive appetite as well as the fact that I am urinating alot. The baby moves alot and kicks all day in different directions and sometimes until the early hours of the morning. Yesterday we went for a scan which took the doctor 30minutes, because she thought she saw four legs and she also thinks that another baby is hiding behind the one baby. How possible is it for twins to be hiding behind another? And, are the terrible backaches, excessive eating and hectic kicking in different directions a sign of twins?