This is a very common problem but one that is easily fixed.
What's happened is that you've fallen prey to the marketing propaganda of the meat and dairy industries. Don't worry, it's not your fault. Agribusiness is dependent on you buying their products and with very powerful lobbyists working hard in Washington, they've managed to convince the U.S. government that the best thing for the country is to promote meat and dairy as absolutely necessary. In fact, the USDA has been persuaded by agribusinesses that protein is THE most important nutrient in the human diet. They, in turn, have passed that on to us, when, in fact, that is the farthest thing from the truth.
Every time you watch television or go to a movie or read a magazine, you are bombarded with the product of this campaign. We are constantly being led to believe that the human diet should consist of a huge slab of meat, some bread and potatoes, and if you're forced to eat them, you can have a fruit or veggie, but those are of little consequence. Once you decided to give up the meat and just stick to dairy, eggs and veggies, you brought that programming with you and very likely, you're eating way too much dairy.
When you were a meat eater, all that heavy meat was hard to digest, so it stayed in your system longer and you ate fewer meals. Now, you've started substituting dairy products for the meat you used to eat. There are two issues with this that have caused the weight gain. First, dairy is very fattening. According to Dr. Joel Furhman in the film Fat, Sick and Nearly Dead, your stomach is lined with fullness receptors that tell you when you've had enough and can stop eating. With vegetables, a 400 calorie salad entirely fills the stomach, telling you that you are full and don't need anything else. A 400 calorie piece of meat might fill the stomach half way telling your brain to keep eating. But 400 calories of fat or fatty dairy products might only fill your stomach about 20 percent of the way and your brain thinks you need quite a bit more food so you keep eating.
The second is that the human body needs much less protein than we've been led to believe. For more on this, watch the TEDtalk given by Mark Bittman here. It isn't as simple as just not eating meat. We have to retrain ourselves not to believe the meat and dairy propaganda.
Losing the weight and getting back on track is just going to take some minor adjustments. Instead of eating more dairy in place of the meat you used to eat, add more veggies and fruit to your meal. Cut out as much of the high fat dairy as possible and when you do eat dairy; go for something low in calories. Go for a 1/2 hour walk every day and, with a drastic reduction in your dairy intake, the weight should come off in no time at all.