How to handle my child with adhd

My 8 yr. old daughter has adhd, and took concerta for about 4 months. She was switched to daytrana. I am having a really hard time with disciplining her. I can't tell if she can help "acting out" or if its part of the adhd. I'm new at this and trying to research it all. I am 27, and a few months ago I had a total hysterectomy, due to endometriosis, and they took both ovaries as well as uterus, tubes, and cervix. I am not on ANY hormones right now, and I am experiencing major hot flashes and irritability. I am also a full time student trying to get into nursing school. I feel like sometimes I just "fly off the handle " at some of the things she does, and later I feel terrible, like I'm this horrible mom for yelling at her. She has a hard time focusing, and when i'm talking to her she tends to just turn her head and look around the room. I take this like she's ignoring me. And when i'm telling her that if the behavior continues she's getting grounded or something, she all of a sudden just interrupts me, like she's not hearing anything i'm saying. That makes me crazy. I feel like i'm failing her, as well as my 6 yr old daughter who I feel is not getting enough of my attention because i'm always spending so much time getting on to my 8 yr old. I am researching different discipline tips and parenting ideas. This is all just becoming so over whelming for me and her too i'm sure. I'm trying to deal with surgically- induced menopause, 2 children (one with adhd) and a husband who was away at the police academy for 4 months. I'm hoping this is a place where I can find some sanity from people who are dealing with similar issues or have ANY suggestions!