DH, I tried doubling my does of Cymbalta too to overcome SAD symptoms but it also made me just want to sleep all the time. My cousin then told me about Wellbutrin. It is often prescribed specifically for SAD. Anyway, I mentioned it to my doctor, we gave it a whirl and it worked great (in addition to my orginal dose of Cymbalta).
Lexapro can also have a sedating effect. Effexor has an energizing effect for most people. I loved it, but I had a side effect of it thinning my hair out so I went off of it.