Losing weight before getting pregnant..

Hi guys, I am TTC with my husband and found I've gained back 18 of the 25 pounds I lost over the spring and summer last year before my wedding.  I'm struggling to lose it again in hopes of not only TTC but a better & healthier me. I am typically active in nice weather but winter is awfully cold and although I do crossfit x3 a week and track my eating, I'm still struggling to lose more than 5 pounds because I then plateau! I'm very frustrated and it mentally wears me down. Any advice or ideas to help kick start it again would be great! Thanks!