In my view, the key to having success with SSRIs is:
1. Avoid the bad ones, especially those that have anticholinergic properties. The SSRIs worth trying are escitalopram, sertraline and fluoxetine.
2. Start low and go slow. SSRIs are often overdosed. 1/4 - 1/2 regular dose is usually enough for a substantial improvement in mood, while avoiding side effects.
Some side effects in the beginning is normal, even for people without ME, and include restlessness, gastrointestinal issues and insomnia. They usually pass after about 2 weeks.
I tried all three, but only tolerated fluoxetine. I started at 5mg, and after 8 weeks increased to 10mg. I have tried 15mg a few times, but do not tolerate that dose. The regular dose is 20mg.
Pre-ME I tolerated Citalopram, so maybe I should give low dose Escitalopram a go. MY last doctor put me on Cymbalta and that was just crapola. I suspect I don't even have low norepinephrine.