I am trying to calculate the two and three-loop divergences in a certain quantum field theory.  This is beyond the domain where I can do anything by hand, and I would appreciate any recommendations for software.

One difficulty is that the theory I am considering is non-Lorentz invariant -- Lorentz symmetry is broken by a background field.  As far as I can tell it is hard to implement this in most packages. 

Any help is much appreciated!