I took Wellbutrin in addition to Zoloft for a short period for exactly this reason. Unfortunately, the Wellbutrin was too "speedy" for me. It turned out that my diminished libido probably wasn't due to the Zoloft but due to lingering depression and unresolved issues between my spouse and me. Exploring those issues in therapy, recovering more fully from the episode of depression, and exercising regularly got my libido back to normal.