There could be two things going on with the frequency of vivid dreams that aren't directly related to the food you eat. The first is that you may suffer from anxiety because you're making a big change in your life. This probably won't manifest conciously because you're happy about it, but in your subconcious, change is change and that's stressful. The other (and this is a little bit about food) is that your brain may be functioning more clearly, and you're just remembering more vivid or disturbing dreams than you did before.