My biggest problem is the lack of assertiveness, it's like I'm too fearful to say no and even at work I just treat my coworkers like I would treat my boss, just to keep them gentle to me.

Well; I often end up to give help for nothing at all.

EX : coworker broke his car and since we work together I decided to take him from home to work everyday, and then back home. He doesn't even live near me, around 30 kms from my house and 15 from work. Sometimes I didn't even ask him some money for the fuel. What can I do? How do you call my behavior?