Ipad 2 won't backup to icloud

[halltiwanger]

I keep getting messages that my ipad hasn't been backed up in weeks. At this point it has been 4 weeks and I don't know why it won't backup. It is always connected to wifi and charging at night. I have even gone into settings and plugged it in at night while connected to wifi and told it to backup, but it hasn't worked. What should I do?