I did it last Summer, I mainly did it to pay for school. It wasn't easy. Fortunately, my day job provided me with some relaxing time and some fun. The night job was ok but it was a lot of grunt work. Nonetheless, I did make good money in one Summer. But it is true what one of the posters mentioned above, you do get sucked into working. You don't even realize it until it's over, I worked two jobs since I got out of school unti the end of the summer. I was invited twice to go to the beach by my friends and I turned them down because I felt like I had to work. It also tires you mentally (it doesn't matter what type of job it is, it always does). Once I started school again, it wasn't until halfway through the semester that I realized that I was making stupid errors in exams, not being able to concentrate and not even realizing it. When I figured out that it was because I was tired, I decided to relax. Started working less and going out more often and my grades went up again. I was planning in doing it this summer again, but something unexpected (and better ) came along so I will no be doing it again.
GL in whatever you decide.
Regards
ng
edit: Now that I am reading your posts, I 'd say that it wouldn't be a good idea for you to get a second job. You need a high level of motivation to do it, a goal that you want to achieve (in my case it was to pay for college so I wouldn't have to work hard when I am in school). What you need to do is work in your self-esteem, then you need to set a goal for you. Friends can be the best thing that one person has, but how can you expect everyone else to like you when you don't like yourself?. I'd recommend you to start working out, going out to run in the mornings. Try to figure out what you want to do with your life and then work from there.