I've been a vegetarian for years and years. Not for health reasons, but for ethical reasons. I grew up on a farm and could never stomach slaughtering my own food or living with the guilt of knowing that I'd taken a life. I figure that if I am not willing to kill it myself, then i probably shouldn't eat it.
I was vegan for around two years but found it very hard to keep my macros balanced, so instead (now that I live in a city and on the other side of the country from my parent's farm) I sought out ethically raised eggs (from free range chickens - I go to the farm myself to collect my eggs) and dairy from happy, field grazing cows and goats (I don't milk them myself, but I do go to where they live to pick up the dairy), which has afforded me the opportunity to learn how to make my own cheeses and yogurts, which is awesome, especially with yogurt, since I can control exactly how much sugar is in it.
As a vegan, it is very easy to eat a lot of carbohydrate, because carbs are from vegan sources. Beans and lentils, tempeh, even faux-meats and some faux-cheeses, are carbohydrate heavy. You'll have to learn how to cook using plain tofu, seitan, nuts, and seeds, and when you do use other sources of vegetarian protein, it is best to make sure that the rest of the calories in your meal come from lower carbohydrate vegetables, rather than adding a carbohydrate on the side (so your plate might be 3/4 veg). Also, be careful with vegan milk, as most have added sugars, so you'll want to seek out "no sugar added" variants. Also, most vegan milks are fairly low in protein, so they really don't help much with balancing your macros. Furthermore, look into getting some nutritional yeast to make sure that you are getting your B12s. Marmite or vegemite is also a tasty choice (maybe, you'll love it or you'll hate it) for B vitamins. And remember than, while mushrooms are awesome for adding meaty texture, they don't provide much protein, so you will want to make sure a protein source is still present in the meal.
You have to be careful with fat too, because you'll probably have to make a conscious effort to get enough (unless you are eating lots of nuts, seeds and avocados - in which case it is easy to over do it on the fat). You'll want to make sure that you are getting varried sources of vegetarian fats to balance your micros (before going vegan I used only olive oil, but I got fat from animal products as well). Flax is a great source of omega-3s, and can be used to replace an egg in recipes. Coconut oil can often be used in place of butter (and is delish on air popped pop corn).
If your tired all of time, you might not be getting enough iron. Good vegan sources of iron include: beans and lentils, tofu, almonds, tahini, quinoa (also has protein!), bulgar, millet, sunflower seeds, green leafy vegetables (spinach, bok choy, swiss chard, turnip greens, kale or broccoli).