"I am not giving up seafood" Then you aren't really a vegan. Vegans don't consume or wear products from animals. This includes not eating honey or gelatin or wearing leather or wool. Believe me, if you tell a vegan that you eat seafood, many will get riled up.
I've been a vegetarian for more than 10 years. Initially, I included dairy and eggs but no seafood. I used dairy a lot for protein. In the past year, I gave up the dairy (infrequent cheats for cheese or ice cream) and added seafood and kept eggs. The balance is working out much better for me. So, technically, I'm a pesce-, ovo-vegetarian. You would be a pescatarian. And some people will argue that those who eat seafood aren't even vegetarians.
I'm not sure why you would have low energy. Short-term that comes much more from carbs than protein. I do take a multivitamin with high levels of B vitamins to keep on top of that but it would take more than a day or weeks even to develop a deficiency. Since you aren't doing this for ethical reasons, I would ease into it more slowly to allow your body do adapt.
However, I'm not sure this will bring you closer with your future DIL, especially if your "secret" plan is to get her to eat healthier in preparation for birthing your grandchildren. There are lots of benefits to not eating red meat, pork or chicken. The focus should be your own health and well-being.