There are a number of things that could be going on here. I'm no expert but a couple of things spring to mind.
1. You may actually have some illness. I get the feeling you are trying to discount this but it is a possibility and I do think it's worth a trip to the docs. You are 19 and at an age where glandular fever is not uncommon. I had a virus (similar to glandular fever) in my early twenties and my symptoms were not dissimilar to yours. I felt not quite right for months afterwards. Having said that, these symptoms are quite generic and could indicate lots of things. Related to that, you may have mild depression but you'll no doubt know if that's likely to be the case. For a case of the blues or more mild depression, I've found that taking St. John's Wort helps quite significantly.
2. A few things jumped out at me about your diet. You are eating a lot of processed meat (sausages, bacon, salami) and very little fresh meat. I realise you need to eat cheaply but you would be better off foregoing the bacon etc. and incorporating some chicken into your diet. Also, you really need to eat fish. Even if you don't eat any meat, you need oily fish for the amount of exercise you are doing. Fish is good for the joints and the brain, which as a cyclist and college student are essential. Eat lots of mackerel, which can be bought cheaply and eat salmon too. Next up - vegetables. As someone else on here said, don't boil them as all the goodness goes into the water and very little is retained in the vegetable. This makes canned veg pretty rubbish I'm afraid. Try to steam or roast all your veg and buy fresh. Forget the supermarket - get yourself down the market later in the day when they are flogging off the veg. You'll get it cheaper than canned veg and it'll be so much better for you.
You also need more fruit, more than an apple a day. Try to eat a banana every day too and berries. Berries of course can be expensive but blueberries are superfoods and worth investing in. You can buy frozen berries from the supermarket (check the label to ensure they haven't got added sugar etc.) and use them in smoothies - half a banana, handful of frozen berries, scoop of frozen yoghurt and some orange juice (not from concentrate). Bang these in a blender (a good investment for juices and soups) for 30 secs and you've got a delicious smoothie.
It sounds like you are doing pretty well on the grains and if you aren't already, get some beans in there (aduki, flagelot etc.). Buy these dried in bulk as it's cheaper this way and soak overnight. You have to be organised but you'll save yourself a fortune.
Another bit of advice about preparing food, buy yourself a slow cooker. They are cheap (about £35), you can throw everything in it in the morning and the best part is that all the moisture is contained within the cooker and so you don't lose any of the goodness. Because the food is slow cooked, you can buy cheaper cuts of lamb and beef and they will taste great. Throw in dried beans or pasta to bulk out the casserole and any veg you have in the house (it's a great way to use up veg you don't know what to do with). For sauces, use beef stock, veg stock or tinned tomatoes. Flavour with chilli, tabasco, worcestershire sauce, basil, garlic whatever you have lying around. Make enough so you can take it to college the next day or freeze for later in the month etc. Believe me, this is such an economical way to cook and you'll be getting all the nutrition you need.
I do hope you manage to sort this out as I know how it feels to be tired all the time and feel low. Feed your body some good stuff though and I'm sure it will repay you the favour!
, don't know what to do with it, I've got an unopened can of chicken gravy. 
