I've got multiple diagnoses as well, major depressive disorder, GAD, ADD, complex PTSD, OCD, substance abuse disorder....the aim is to find just one or two medications that help with everything. And it is possible. Like I said earlier, I take Cymbalta, and usually I take topiramate as well, which acts as a mood stabiliser. But I'm pregnant and can't take the topiramate while pregnant so I had to cut that one out. I'll continue it after I give birth though as it really helps me.
For REALLY effective help and relief of your symptoms though, incorporating some long term therapy as well as taking meds is your best option. Medications alone can simply act as a bandaid, which is okay for a while, but therapy will really help you get effective relief.