Hi there MissTired. I was on lithium for about 2 years after birth of DD. I had really bad PND which didn't seem to respond to ADs, so they put me on lithium as a mood stabiliser.
I have to say I was petrified when they said they wanted me to go on lithium. I was an inpatient in the mother and baby unit at the time and felt completely vulnerable and out of control with regards to my treatment.
I was sent for an ECG (I think they have to check your heart before starting lithium) and various blood tests. Then the bloods were repeated after I'd been on it a few days to check how my body was metabolising the lithium.
I had to have 3 monthly blood tests then for the duration I was on it.
I have to say, despite being terrified, I never had any particularly bad side effects on it. Maybe a bit sicky for the first few days and that was it. I was discharged from hospital about 2 weeks after starting it, and felt a bit better. Don't know if it was coincidence, but I did start to improve once I was on the lithium.
Once I had been better for a while I decided I wanted to come off lithium, as I was worried it might do some long term damage to my kidneys. It was a bit of a struggle to persuade the psychiatrist to let me come off it, but am so glad I did, as I came off it in May and have been fine mood-wise ever since. Am glad to be off it, but it did help at the time. Also I didn't find it hard to get off (no withdrawl effects) unlike my AD which has been a long drawn out process.