General Advice

[OYourBlind]

Hey Guys,
I'm 22, 5'9 (from memory i'm 174cm) and weigh 87 Kilos (190 Pounds).
I've been on and off with the gym since I was about 15, but alot more off than on.
I have a fair few questions. I'd say i'm a about 4-7 kilos (8-15 Pounds) overweight for my size.
I was fairly active throughout my sporting season training maybe 3-4 times a week with 4 different sports, and playing sport all weekend. I have a pretty poor diet but it wasn't noticeable through sport, until now it's off season and i've noticed a slight chance in size.
I'm a member of a gym, I havn't been for about a month, and i'd say i've been maybe a total 3 months out of this year. Motivation is my key! I've found I'll keep going but once I miss a day or 2 for some reason, i'll stop going, and without a training partner to drag me to the gym I find it hard to get motivation. I'm a University (Collage) Student so time isn't a restraint, but sitting around doing nothing and sitting in class for a short time in the day keeps me unmotivated.
I've done alot of reading about supplements, exercises and diets over my years so I have a decent knowledge of it.

So basicly, I want to lose say 5 kilos (11 Pounds) or atleast notice a difference in my body fat percentage. I know size is something that comes with time, but I do really want to put on size and stay motivated.
So my questions are..
How do you guy's keen yourself motivated, especially when you train alone?
What diets, or things I should and shouldn't eat? eg Carbs
Basically any information I can take away from this and use for myself in practice. I can take photos if needed.
Cheers.
Daniel