I've been having trouble sleeping lately...?

Okay, so i'm 14 and awhile ago.. around 2-3 weeks back I had a nightmare. And ever since, I haven't been able to have a good sleep. Just the other night, I went to bed at around 9-9:30pm and I wasn't able to fall asleep till 4:30am and I was awake again at 6:30am. So i only got 2 hours sleep. And then had to goto school, which was horrible because I was on the verge of fainting or ping out from being so tired. My mum tells me to goto bed earlier, but it dosn't matter how early I goto bed, the same thing happens. Ever since that nightmare! and I just want a good sleep because its not helping me with being able to concentrate during school etc. People have even said i'm getting snappy and rude lately because of the little sleep and normally i'm polite and friendly... Can someone please help?