Lamictal acne side effect is just one of rare side effects of this drug. According to Wikipedia

Lamictal side effects may include acne and skin irritation, vivid dreams or nightmares, night sweats, body aches and cramps, muscle aches, dry mouth, fatigue, memory and cognitive problems, irritability, weight changes, hair loss, changes in libido, frequent urination, nausea, and other side effects. In very rare cases, Lamotrigine has been known to cause the development of a dangerous rash called Stevens-Johnson syndrome (or SJS). The rash is more common in children, so this medication is often reserved for adults.

LAMICTAL has been administered to 6,694 individuals for whom complete adverse event data was captured during all clinical trials, only some of which were placebo controlled. During these trials, all adverse events were recorded by the clinical investigators using terminology of their own choosing. To provide a meaningful estimate of the proportion of individuals having adverse events, similar types of events were grouped into a smaller number of standardized categories using modified COSTART dictionary terminology. The frequencies presented represent the proportion of the 6,694 individuals exposed to LAMICTAL who experienced an event of the type cited on at least one occasion while receiving LAMICTAL. All reported events are included except those already listed in the previous tables or elsewhere in the labeling, those too general to be informative, and those not reasonably associated with the use of the drug.

If you experience lamictal acne side effect don’t stop the Lamictal just lower the dose. It is common to need less of a medicine to sustain improvements after an acute episode of difficulty. The decrease should occur slowly. Skin takes a while to heal and adjust to medication changes. I would recommend decreasing to 100 mg for a few months and then, if needed, more cautious tapering (eg by 25 mg every month or two). You are really balancing how you feel with improvements in your skin condition. If, as you decrease the Lamictal dose, your acne remains bad and your mood begins to become more depressed . . . you have a difficult choice to make.