S.C.
I had a similar problem with my son and used a little tough love. We have a strick routine with bedtime (7:30 an alarm clock goes off) so they know it is time. We take bath, read a book, say prayers and go to bed. When he cries I give him 15 minutes and then go back and tell him it is time to go to sleep, and keep doing this with less frequency until he goes to sleep. This took me about three nights, but it worked like dream. Sorry you are having this problem, espeically if you are a single mother, that has to be terribly hard.
I have found that even when things don't work, as long as I am consistent, it helps them, ultimatley feel secure.
This to shall pass....