You can be treated for Bipolar without the use of an antidepressant. If you are on an antidepressant, usually the doctors want to have you on a mood stabilizer (i.e. Lithium, Depakote, Lamictal) as well to help counteract the risk of mania. From what I know from the research, antidepressants don't necessarily trigger manic episodes for most people, they just make it easier to flip into them if the conditions are right. So, doctors are often hesitant to use them.

Lamictal can indeed help with depression. Other mood stabilizers can as well. If you're still feeling depression on your mood stabilizer, your doctor could consider augmenting with an antipsychotic as well.

I was on Lamictal but still feeling depressed. We tried adding Wellutrin but it was ineffective. We then switched to Latuda (an antipsychotic) and it was a dramatic benefit.