Can someone explain this?

I have thought about this the entire day, but still I haven't come to some kind of conclusion, and I guess there is no correct answer, but I don't understand it. I have had a lot of things going on for a while now, almost too much. School work, work, school, different kind of things, you get it.

 Now I realize that have been too much so I have to take it more easy. People are calling me all the time, and I know I sometimes have to say no, or maybe I should say: some of these people are calling me several times a day and it's kind of taking my energy to answer all these calls. That means that i have to say no, in the weekends I have to like do things I like because otherwise I don't have enough energy for all the things I do from Monday through Friday. That doesn't mean that I sleep through the weekend, but I don't want to work every singe day of the week. This means that I have to say no if someone for example ask me if I can help them with their computer. Ok, this is something I don't want to do, and it makes me tired, not happier at all, not even a better person, and I kind of know that this person wont be very thankful either. But If I do this to everyone, I'm not kind of used to it yet, how can I then trust others and believe that they will do things for me if I ask them?

I know you can't always say yes, and do things for others and get nothing in return, but I don't want to be egoistic, and how do I know if I am? At present I have a friend and it feels like I have done pretty much for her, and she has done pretty much for me, but still I feel like I can't trust her because she is always saying no in some kind of weird way even though she never say the word. And gosh, I don't want to be like that. How do you know where to draw the lines? I guess there is no answer, or there is, but there is more than just one.

Today a person I met at work accidentally slammed the door right in my head, I kind of bounced against the wall and it felt like my back twisted itself, I hope I wont have a huge bruise above my eye when I wake up tomorrow *laughing*. It had never happened to me before (just a note: The door was made of heavy steel) Hehe!

I think I know now, trust your gut feeling. It's not harder than that, no one can be perfect and if someone is really mad at you, you can only hope they will tell you about it.