Back at work

Well, I have been back to work for 2 weeks now and I have to say it is not that bad. I am surprised by that because when Sonia was born I did not go back to work until she was about 5 months old. It is very different from Sonia because I had to leave Sonia with strangers at a day care center in CT while I traveled to MA for my job. I worked 10-6 so Rich had to pick Sonia up. This time, my mom is taking care of Nicholas and I feel so much more at ease. I am not woried all the time and I can go to her house to see him on my break.
The parents have all welcomed me back and are happy that I am back. The kids have acted like I never left and to be honest I don't know if that is a good thing or a bad thing.
I sleep pretty good. Nicholas gets up once in the middle of the night and then just about the time I need to get up to take a shower so that works out well.

What am I doing wrong!! HELP!!!

I do not know what I am doing wrong; but Sonia will NOT sleep in her own bed/room. I lay down with her and rub her back and when I try to leave she starts crying and says her belly hurts and she needs to throw up. When we arrive at the bathroom she cries and says she wants Daddy and to sleep in Daddy's room. Now, I have been laying down with her for almost an hour and I thought she was a sleep but NO!! I get extremely aggravated because I am tired and she used to be fine going to sleep after I left her, but ever since about June of last year she has had to have me lay down with her until she has fallen asleep. I don't know what to do. I have tried all my "tricks" I think I know but they have not worked! HELP!