ever in the world did I think I would EVER take advice from a DEA.
*laugh* I needed a domain name and thought it would be funny late one night...it's been causing confusion ever since.
I don't have a gym membership (too expensive
Unfortunately, it's going to cost some money to build real muscle. Money for food/protein, money for a gym membership or home equipment.
Gym memberships can be had for about $30/month in most areas; if you're serious about getting in shape, it's a small price to pay. Call around to local gyms and see if they offer day passes or trial memberships (tell them you're looking for a gym to join but don't want to make a decision until you've had a chance to get a good feel for the gym; they can probably arrange something.) It's worth trying a real gym just to familiarize yourself with the sorts of equipment/exercises out there.
If you find yourself thinking of home equipment (and have the space for it), take a look at this thing:
http://www.gymcor.com/powerrack.html
It's called a power rack. They're used for all manner of exercises; you can do pullups on the frame, safely bench press, squat, etc. If you could only buy one piece of equipment, it should be a power rack IMO. (Well, you'll also need an olympic weight set and probably a bench to stick inside the rack.)
If you go to a gym, make sure it has either a power rack or a squat rack (something similar to
this thing.) A Smith machine (a device where the barbell slides up and down in a track) is NOT good enough in my opinion.
Study muscles. Figure out where everything is and WHAT IT DOES. For instance, which muscles are used to bench press? Most people would say 'pecs', but that's not even close to the whole picture. Perhaps the most important muscles for benching are the triceps (the muscles under your arm, opposite the biceps.) The triceps job is to straiten/extend the arm, making them critical for any pressing/pushing movement.
Read more here:
http://www.bodybuilding.com/fun/anatomy.htm
Don't neglect your back! Learn how to do barbell rows and pullups. (If you can't get to the gym and don't have the budget/space for a power rack, you can get a fairly inexpensive pullup/chinup bar that mounts in a doorway at Walmart or such.) The lats (the main muscle worked by pullups) are a big part of what gives your body that broad shouldered, v-tapered look.
Honestly, I'm not following my caloric and protein intake
Time to start.
When you're building muscle, you're going through two stages. First, you lift weights to cause tiny tears in your muscles. Then you sit and relax (and eat) while your body repairs and reinforces the damaged muscles. (This process is what causes next-day soreness.)
Rest and diet are every bit as important as your workout. If you don't give your muscles enough time to recover, they won't be able to grow. (Generally people don't target the same muscle group more than twice a week, and often only once a week.)
During the repair/growth phase, your muscles need plenty of protein and calories. If your body doesn't have plenty of calories available, it will try to conserve energy by limiting muscle growth. Protein poses a special problem; if there isn't protein available, repairs/growth can't happen, and since your body doesn't have a way to store protein, in order to maximize muscle growth you need to provide your healing/growing muscles with small amounts of protein throughout the day. Bodybuilders will usually eat about every two hours. (Small meals, protein shakes, etc.)
So: Eat more, eat more protein, eat more often.

(And plenty of sleep too.)
Do NOT skimp on diet. Lifting weights without a good diet is like buying a sports car with no wheels; you won't get far.
I don't think I'll buy the creatine (what, with all that water-muscles and all that)
Personally I haven't noticed any water retention, but it's hardly critical to include.
I do as many reps as I can (keeping the max reps I can do at 13-15)
I would probably increase the weight a bit (reducing the reps to perhaps 8-12.) Not using heavy enough weights (and not increasing them aggressively as your strength grows) is one of the common (and serious) mistakes newbies make. Many lifting programs involve increasing the weights every week whether you feel up to it or not.
My own goals are brute strength, so I generally choose weights I can only lift for about five reps (some advanced strength athletes only do 1-3 reps with very heavy weights.)
and that one that you push your elbows together. (lol, such a noob) butterfly?
Ah, the hated 'pec deck'. IMO they put unnatural and potentially harmful forces on your shoulders; I'd look for a different exercise.
Also, I do roughly 100 pushups a day just because I think it will help.
The trouble is, if you're strong enough to do many reps of an exercise, you're no longer very effectively challenging (damaging) your muscles, and without that damage you won't get repair/growth. To make pushups more challenging (and thus more beneficial) add resistance. They sell latex resistance bands for exercise; you can loop them over your back to your hands, making the pushup harder, or you can add weight (such as by putting a sand bag on your back.)
It's critical to push the limits of your strength to effectively build muscle. Lift heavy, eat well, sleep as much as you can, repeat. That's it in a nutshell.