I had about 3-4 weeks of not feeling very good. Like you, I had low energy, mood swings, and my body had a lot of painful transitions. I had cramps, migraines, etc. After that though, I have felt better and better every day! I've only been Vegan for about 4 months now, but I am so happy I pushed through that detox time in the beginning.
Keep going -- you'll get there! Also, I've read from other people that it's a good idea to get some blood work done to make sure you're getting all the right vitamins and nutrients. I haven't done that yet, so I don't know much about it. But, there is a lot of great info detailed in the thread below yours in the 'Vegan Results' Forum.