The art of Concentration

My short-coming is low concentration , you know, it's driving me crazy since I can't be as efficient as I expect of myself, the truth is I wanted to be practical and physically active and I've been interested in talking English so I took the English courses since the first semester of university and I also did a lot of sports like parkour, aerobics, basketball, gymnastics. I did bike riding and mountain climbing for fun. It didn't last  much, I chose gymnastics as a sport(although it was too late for a 20 years old girl but any way I didn't want to win the championships!) and continued English as a necessity for my major and something fun for myself.On the other side I didn't want to be overweight just like my mom, I wanted to be slim and sporty but I couldn't make it once I got slim and little by little I got weight. It seems like my eating habits are turning to yo-yo diet! I'm slim for a while and a bit overweight for rest of days, because this is the way I've been brought up and I love to eat as it's an opportunity to get together and not to think about problems, I'm losing my mind, I feel I can't make doing "What I really enjoy", everything just makes me frustrated, all the time I have assignments but I really don't learn anything because I'm just doing homework, besides I can't simply leave collage and trust on myself to make a different life, what should I do? I'm getting crazy, I had this problem since high school when I lost my chance to do what I like, I'm really worried for myself, tomorrow is the day I have to take my "Numerical Computation" assignments to university and give them to professor, I haven't done them yet and I won't make it tonight because I've completely forgotten the lectures since the professor was absent last session, on the other hand I have part time job and I'm busy in the evenings with that so I just have odd day mornings free to study a bit and I have English course on odd day mornings and I do English assignments after class then I have lunch, make something ready as my dinner and I head  work and I arrive home around 9:30 or 10 pm. I can't stop working because it's  what I really enjoy to do at least, I enjoy helping the others and really do something with my hands, I have my own income and I can buy whatever I like and also save money and make plan for spending and saving the money, I can't concentrate because I feel I've to conform my professor, my English teacher and etc. I don't feel free enough  to do my best. What should I do? someone helps me I'm freaking out.