labor over (something)
To put in a lot of time, energy, and effort to successfully accomplish or complete something. I've been laboring over this dissertation for months now. My wife likes to plan every minute of our vacation, laboring over the tiniest details.
labor over someone or something
to work hard on someone or something. The surgeon labored over the patient for four hours. I labored over this painting for months before I got it the way I wanted it.