Vegitarian after Keto?

I'm on the Keto diet for the second time. I lost 50 pounds then went on a vegetarian (eating eggs and dairy) and started gaining weight! So I'm back on it but I prefer to be vegitarian. Any advice on how I can avoid weight gain? I still avoided junk food before and only have maybe 3 sodas a year since I don't like them that much. What am I doing wrong? I exercise moderately.