Can I take probiotics with my meds for BiPolar II, Cymbalta (duloxetine) and Lamictal, or does that risk increasing Seratonin levels?

Probably fine. The major concern with Bipolar medications is the pharmacological interaction that might occur. Because probiotics act locally in the gut, there is no reason to not take them. That said, I'm unsure if they will help you in any way ... But they should be ok to take with Cymbalta (duloxetine) & Lamictal.