Not sure how old you are, but yeah you definitely need to up your calorie intake.
I know it's annoying to do, but you should keep a nutrition journal (at least for a week or so) where you write down everything you eat and the total calories (if you happen to know). You can figure out what your calorie goal is from calorie calculators such as the one posted by exclamatio from his laptop within his hyperbolic timechamber =p
Another calorie calculator (but less elaborate):
Calories Per Day Calculator - Basal Metabolic Rate
If you can't be arsed to write the calories or guestimate them, then just write down what you ate and feel free to post it on here. A couple of days worth should give us a good idea of your eating habbits.
Make sure that you eat useful calories though. Also keep in mind that your portions size matters (such as eating 5 small meals a day vs 2) and that the time in which you eat matters too (eating before you sleep vs earlier in the day while you are active).
Many people have an issue where they cannot eat enough food in a given day (and I totally relate to this). They're usually too full still or lack time. If you lack time, then bring snacks with you. If you're simply too full though, then unfortunately you just have to suck it up and eat anyway. Your body isn't use to eating enough so just like you train your mind, muscles, and heart, you must also train your stomach / metabolism / etc.
On that note, you should take protein shakes. They can be energizing as well and they also add additional calories. Not to mention they're fucking delicious! =P ON Whey protein is what I take. However, if you really want to get into it, also get casein protein. Casein is absorbed more slowly by our body whereas whey is absorbed fast. You probably no where I'm going with this -- take casein before you sleep and whey casually in the day (especially good a bit before/after lifting).
This is definitely not the reason why you're tired, but scientifically speaking, if you do not get enough sunlight every day, your energy levels will drop too and you'll start lacking another vitamin -- vitamin K -- which our entire generation now lacks because of computers and video games. In fact, there was an article before that said this generation is the first generation to have a lower lifespan than the last because of that, but it could be BS.
Another issue, which may not relate to you at all (though IS possible if your food intake is low) is that you could be neglecting an important vitamin. I for one had iron deficiency when I was younger, and that made me tired all the time. It doesn't have to necessarily be iron either, as neglecting other vitamins causes the same issue. I recommend taking a multivitamin in the morning with some food. Keep in mind though that if it IS iron specifically that you're lacking, that multivitamins don't often include iron unless they're designed for WOMEN (they need the extra iron since they bleed every month and need to recoup their blood...).
Anyway -- the short and skinny of it all is to eat more and take a multivitamin. You don't need protein shakes or weight gainers necessarily (they're optional), but they can help a lot if you're willing to dish out the extra cash, which (in my opinion), you should since it is effecting the quality of your life. Being tired all the time is no fun.