It's pretty common to first be diganosed with depression first then later BP. I can't remember too much about my experience with lithium, but I was also struggling with PTSD and dissociation at the same time. It took awhile to stabilize down to a point I only needed BP meds. Lithium used to be the first line med of BP and some doctors are still more comfortable with the older meds that have known long term effects over the newer ones. Only time will tell if lithium alone will work for you.