Lazy nurser??

I have been back at work for about 3 weeks now.  I nurse LO in the morning - then she gets bottles during the day - then I try and nurse her when I get home.  She latches right on, but only nurses for a few minutes and pulls off.  She use to be an aggressive nurser - she has always gotten a bottle here or there, but now I feel she gets the first let down and won't work for the next.  I'm worried she's not getting the hind milk.  Any suggestions on how to get her to be a more aggressive nurser??