For me it's generally blood sugar and waiting too long between breakfast and lunch. Protein generally fixes it pretty quickly, so I would try to find which vegetarian proteins you really like and have some on hand. It is significantly worse when I am pregnant, like normally I like a piece of cinnamon toast or a muffin with a cup of coffee for breakfast. When I'm pregnant anything sweet for breakfast makes me shaky. So right now I discovered some fake breakfast sausage that tastes almost identical so I've been eating it on a piece of bread/biscuit/english muffin. We do still eat some seafood in our home, but we're down to usually no more than once a week (keeping it in got DH on board the rest of the time, we haven't had any meat products in our home for 2 years now
). The rest of our meals are vegetarian or vegan.