Hello Serena!
I'm glad to see you started a diary. It really is very helpful in your journey and will be a place for you to tell the events of your day and get support and advice.
Walking is the best place to start exercise wise. I suggest getting your body acclimated to walking on your treadmill for about 40 mins. At quick pace this can be about 2 miles. Once your comfortable walking at that rate, then start jogging instead of walking. This is how I got myself into running.
If you find yourself getting bored, go for a walk or jog outside. It's nice to pair running inside as well as outside as both have benefits to each.
I understand your feeling when it comes to exam time. I just about go mad everytime! I'm getting ready to start my 3rd year in College (I believe you call it University?) in less than a month. I really hope I can balance all my school work, real work, and new healthy lifestyle.
My motivation to lose weight is to look fit, beautiful, and healthy at my wedding in June next summer. I want to not be self conscious in my swimsuit on my honeymoon and I want to have loads of self confidence. I'm well on my way now and I'm feeling great!
If you need support or advcie, don't hesitate to ask anyone here. We all want to help and support you any way we can! Since we're both in college, perhaps you can check out my diary. I wonder if maybe we have a similar journey. I'd love to hear from you!