Weight and TTC

So after having two kids I had to lose 75 pounds. It's been three years since I lost it all and now I've gained about 30 back. I hate how I look. It depresses me so much. I don't feel that fat.. then I see pictures and it blows my mind how much bigger I look now. I've been trying to diet for a month and haven't noticed any sort of difference yet. But my husband and I want to try for a third. Now is the best time for us and we have decided to give it until March. But I'm so worried and stressed about not losing weight before I get pregnant and gaining even more once I am. Can I diet while pregnant? Within reason of course. Should we wait to try until I'm at a happier weight/ esteem place for myself? Or should we take the plunge and I can worry about losing it after?