Why Parents seem to get mad everytime I schedule my college cles?

Okay. I am a nursing student, trying to complete my prerequisite courses in a local community college. The first comm. college I went to was too far, approximately 24 miles away from my house (back and forth) so, for this summer and for the upcoming fall semester, I decided to register for another Community College, that is the same Miami Dade, but much closer to my house, approx. 7 or 8 miles away. So, I'm still commuting. I believe that I've sacrificed some things in order to get a well-rounded college education. I'm getting an ociate's in nursing, for now and I won a scholarship while in high school, which i use to pay for my cles and for my books, not to mention the fact that I plan on working over the summer and during school to save money. I am 20 years old and will be 21 years old in November 2010. My parents and my brother work. My brother has decided to drop out of college for now, after he's completed his first year, it seems. So he is only working. I try to schedule my cles to fit into everyone else's schedule. I'm taking a cl over the summer from 1-4 in afternoon. For some reason, and I can feel it, I made my parents mad about something or they're concerned about something and just not telling me. They are also very overprotective at times but have become a bit more lenient. IDK. I just want to be independent and achieve my goals. My parents have attended some college, a few credits, but no degress, although they have stable jobs and make enough money that I can't even receive financial aid from the government. What am I doing so wrong? I am responsible, I help out A LOOOT around the house, I walk the dog, I run their errands most of the time, like groceries or buying a needed item/s. Why do they get so damn mad at me..it's like they don't want me to go to school or spend money on it, when I believe it is well worth my time and money.. I am a female, by the way, if that is relevant.