It's hard. I have trouble with my medications too due to the sheer volume of them. Some days it is simply a relief to ignore them.

Have you talked to your doctor about the nausea? Can the doctor offer any other solutions other than "keep taking it"? Maybe there is an alternative you can try, or an additional medicine that can control the nausea, or anything that can help with the nausea?

I'm not familiar with lithium but I do have a nausea reaction with every anti-depressant I take. The nausea is temporary if I stick with it and the benefits stay behind. Talk to your doctor more about this if you can, it's not a good trade off if the lithium treats your depression but has an unlivable side effect for you.