I don't know how long you have been on Cymbalta but, you may want to try a different antidepressant. Some make you gain weight and it can be a lot and some don't, it depends on your body.
Vitamins do help, especially B vitamins. My dr gives me an rx for vitamin B and I give myself a shot once a month. I started out once a week for a month, then once every other week, then once a month. I will always continue just like it's a medicine. It really helps. You can take over the counter, B3, B6, B12 I may have left one out. Mine is all in one. The shot is more potent but the pills will help too.
As far as sleep, if I was taking a med that interfered with my sleep and made me gain weight, I would take a different med because you do have other choices. For me it doesn't make since to take a pill only to have to take another pill to counteract the first pill (for sleeping). In the meantime you could try drinking some Camille Tea or Sleepy Time Tea and see if that helps, no caffeine at all at least 3hrs before bed and don't watch tv and then try to sleep. Read a book and drink your tea to wind down. Just some suggestions. Take care, Crystal
You may likely need a now med but you will have to talk to your doctor. As long as you are still on it, would recommend you take it RIGHT before you go to sleep and not let yourself get back up and eat. I know that may seem difficult but I am gaining weight as well with my Seroquel. I have broken out of that cycle and got back on my diet and exercise routine. Granted I only likely gained a pound or two but I had worked hard to get to where I was and I didn't want to back paddle too much,
Good Luck,
Larry